Pies & TartsItalian-FrenchMedium

Espresso Mascarpone Eclair Bars

Name: Espresso Mascarpone Eclair Bars
Prep time: 40 min
Cook time: 50 min
Total time: 1 h 30 min
Yield: 12 servings
Cuisine: Italian-French
Ingredients: 4 oz (113 g) unsalted butter, cut into ½-inch cubes; 1 cup (240 ml) water; ¼ tsp (1½ g) kosher salt; 1 cup (120 g) all-purpose flour; 4 large eggs, at room temperature; 1 lb (454 g) mascarpone cheese, cold; ¾ cup (85 g) powdered sugar, sifted; 2 tbsp (12 g) instant espresso powder; 1 tsp (5 ml) vanilla extract; ⅛ tsp (¾ g) kosher salt; 6 oz (170 g) dark chocolate (70% cacao), finely chopped; 2 oz (56 g) unsalted butter; 1 tbsp (15 ml) light corn syrup; ⅛ tsp (¾ g) fleur de sel or fine sea salt (optional)

From the MyKitchenBank Kitchen

Crispy choux pastry shells filled with creamy espresso-spiked mascarpone cream, then stacked with a glossy dark chocolate glaze. These elegant bars combine the sophistication of French choux pastry with Italian mascarpone richness and a deep espresso flavor. The result is a sophisticated dessert that looks impressive but comes together in manageable steps.

Prep: 40 min
Cook: 50 min
Wait: 1 hr 25 min
Total: 2 hr 55 min
Makes: 12 bars (one 9×13-inch pan)

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Ingredients

12 servings

For the choux pastry
4 oz (113 g) unsalted butter, cut into ½-inch cubes
1 cup (240 ml) water
¼ tsp (1.5 g) kosher salt
1 cup (120 g) all-purpose flour
4 large eggs, at room temperature
For the filling
1 lb (454 g) mascarpone cheese, cold
¾ cup (85 g) powdered sugar, sifted
2 tbsp (12 g) instant espresso powder
1 tsp (5 ml) vanilla extract
⅛ tsp (0.8 g) kosher salt
For the glaze
6 oz (170 g) dark chocolate (70% cacao), finely chopped
2 oz (56 g) unsalted butter
1 tbsp (15 ml) light corn syrup
⅛ tsp (0.8 g) fleur de sel or fine sea salt (optional)

Equipment (11)

Two large baking sheets
Parchment paper
Medium saucepan
Wooden spoon
Piping bag fitted with ½-inch (12 mm) round tip
9×13-inch (23×33 cm) rectangular cake pan
Large mixing bowl
Electric mixer
Instant-read thermometer (optional)
Shallow bowl for melting chocolate
Offset spatula or butter knife

Steps

Before you start

Preheat oven to 400°F (200°C) 15 minutes before baking the choux.
Have all ingredients at room temperature, especially eggs.
Line two baking sheets with parchment paper.
Have a 9×13-inch (23×33 cm) rectangular pan ready (do not grease).

1
Make the choux dough
- In a medium saucepan, combine water, butter, and salt.
- Set over medium heat and bring to a simmer, stirring occasionally, until the butter fully melts—about 4 minutes.
- Remove from heat and stir in the flour until a thick ball forms.
- Return to medium heat and cook, stirring constantly, for 2 minutes.
- This step dries out the dough slightly so the eggs incorporate better.
- Transfer to a bowl and let cool for 2 minutes so the dough is warm but not hot (you don't want to cook the eggs when you add them).
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Ready when: Dough is warm to the touch and holds together in a ball
Tip: Cooking the dough after adding flour helps it hold more egg and puff taller in the oven.
2
Add eggs to choux
- Add eggs one at a time to the warm dough, beating well after each addition with a wooden spoon or hand mixer on low speed.
- After the first two eggs, the dough will look shiny and slightly curdled—this is normal.
- Once all four eggs are incorporated, you should have a glossy, smooth, ribbon-like dough that slowly drops from a spoon.
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Ready when: Dough is smooth, glossy, and falls slowly from a spoon when lifted
Tip: If the dough looks separated after adding eggs, keep beating—it will come together. Cold eggs added to warm dough incorporate faster.
3
Pipe choux strips
- Transfer the choux to a piping bag fitted with a ½-inch (12 mm) round tip.
- On the first prepared baking sheet, pipe a thin layer of choux dough to cover the bottom of the 9×13-inch pan (you're piping a rectangle the size of your pan, about ¼ inch thick).
- You'll pipe continuous lines or a grid to fill the area evenly.
- Repeat on the second baking sheet—you need two layers of baked choux pastry.
- Smooth the tops lightly with a dampened spatula if needed.
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Ready when: Two rectangles of piped dough, roughly 9×13 inches, on parchment paper
Tip: Piping thin strips lets the choux bake evenly and crisp fully. If the bag gets warm, refrigerate it for 2 minutes.
4
Bake choux layersOven 400°F / 205°C
- Place both baking sheets in the preheated 400°F (200°C) oven.
- Bake for 20 minutes without opening the door—steam is building inside the choux.
- Then reduce the heat to 350°F (175°C) and bake for another 20 minutes, until the choux is golden brown and feels very crisp.
- If the choux is still soft, bake for another 3–5 minutes.
- Remove from the oven and let cool on the baking sheets for 15 minutes, then transfer to a wire rack to cool completely—about 30 minutes.
- The choux must be completely cool and crisp before assembly.
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Ready when: Choux is golden, very dry to the touch, and crispy when you tap it
Tip: Don't open the oven door during the first 20 minutes—steam escaping will prevent the choux from puffing properly. The choux must be completely cool before filling or it will soften the cream.
5
Make espresso mascarpone cream
- In a large mixing bowl, combine cold mascarpone, sifted powdered sugar, espresso powder, vanilla extract, and salt.
- Using an electric mixer on low speed, beat until smooth and light—about 2 minutes.
- Do not overbeat or the mascarpone will become grainy.
- Taste and adjust espresso intensity if desired.
- The cream should be thick, spreadable, and richly flavored.
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Ready when: Mixture is smooth, light, and no lumps of mascarpone remain
Tip: Keep mascarpone cold and don't overbeat—even 30 extra seconds of mixing can cause it to split. If it does split, it's still edible but will be slightly grainy.
6
Assemble the base layer
- Place one cooled choux rectangle into the 9×13-inch pan (it should fit snugly).
- Spread half of the espresso mascarpone cream evenly over the choux layer with an offset spatula or the back of a spoon—about ½ inch thick.
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Ready when: Cream is evenly spread in a ½-inch layer over the choux
Tip: If the choux cracks slightly, don't worry—the cream will hold it together.
7
Layer and fill
- Top with the second choux rectangle, pressing down very gently so it sits evenly on the cream.
- Spread the remaining espresso mascarpone cream over the top layer, smoothing it into an even ½-inch layer.
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Ready when: Two choux layers with mascarpone filling in between and on top
Tip: Press the top choux gently to anchor it, but don't compress it—you want to keep some air between the layers.
8
Chill the assembly
- Cover the pan loosely with plastic wrap and refrigerate for at least 30 minutes.
- This firms up the cream so it won't shift when you slice and glaze.
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Ready when: Cream feels firm to the touch when you press the top
Tip: You can prepare the bars up to 6 hours ahead and chill until ready to glaze and serve.
9
Make the chocolate glaze
- In a shallow bowl, combine finely chopped dark chocolate, butter, and corn syrup.
- Set the bowl over a pot of barely simmering water (double boiler method), making sure the bottom of the bowl doesn't touch the water.
- Stir occasionally until the chocolate and butter are fully melted and smooth—about 3 minutes.
- Remove from heat and stir in the sea salt if using.
- Let cool for 2 minutes so the glaze is warm but pourable.
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Ready when: Chocolate is melted, butter is incorporated, and glaze is smooth and pourable
Tip: Keep the water under the bowl at a gentle simmer—too hot and the chocolate will seize. If the glaze breaks, add a teaspoon of butter and stir gently.
10
Glaze the bars
- Pour the warm chocolate glaze over the chilled assembled bars and spread with an offset spatula into an even layer.
- Work quickly but gently to avoid disturbing the layers beneath.
- Make sure the glaze covers the edges and sides of the pan.
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Ready when: Entire top surface is covered with an even layer of glossy chocolate glaze
Tip: If the glaze is too thick, let it cool 1 more minute. If it's too thin, reheat gently over the double boiler.
11
Set the glaze and chill
- Refrigerate the glazed bars for 15 minutes, until the chocolate is set and firm enough to cut cleanly.
- You can also place them in the freezer for 10 minutes to speed this up.
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Ready when: Glaze is no longer glossy and feels firm when gently pressed
Tip: A chilled glaze cuts cleanly without cracking. If you cut warm glaze, it may smudge.
12
Cut and serve
- Remove the pan from the fridge.
- Using a sharp, hot knife (dip it in hot water and wipe dry between cuts), cut the bars into 12 equal pieces—3 rows lengthwise, 4 rows widthwise.
- Wipe the knife clean between each cut for a pristine edge.
- Serve immediately or store in the refrigerator.
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Ready when: Bars are cut into 12 clean-edged rectangles with visible layers
Tip: A hot knife melts the chocolate slightly, allowing clean cuts. Cold bars cut more crisply than room-temperature ones.

Good to know

Tips

Choux pastry is forgiving once baked—minor cracks or uneven browning won't affect the taste, and the cream filling will hide imperfections.
Don't skip cooling the baked choux completely; warm choux will soften the mascarpone cream and create a mushy bar.
The espresso flavor deepens as the bars chill, so they taste better the next day. Make them a day ahead if you can.
For a caffeine-free version, substitute the espresso powder with 2 tablespoons of unsweetened cocoa powder or omit it entirely for vanilla mascarpone bars.

Make ahead

You can assemble and chill the bars (before glazing) up to 6 hours ahead, covered in plastic wrap in the refrigerator. Glaze them within 2 hours of serving for the best texture.

Storage & reheating

Store covered in an airtight container in the refrigerator for up to 3 days. These bars don't freeze well due to the mascarpone filling, which separates when thawed. Serve chilled or bring to room temperature for 5 minutes for a creamier bite.

Substitutions

mascarpone cheese, cold → crème fraîche mixed with softened cream cheese (1:1 ratio). Use the same total weight. This will be slightly tangier and less rich but still creamy.
instant espresso powder → strong brewed espresso reduced to 2 tablespoons, cooled. Mix it into the mascarpone with a pinch of instant espresso powder for depth. Reduce sugar slightly as liquid espresso adds moisture.
dark chocolate (70% cacao) → milk chocolate or a 50:50 blend of dark and milk chocolate. The glaze will be sweeter and less bitter. Use the same weight.
light corn syrup → honey or light agave syrup. Either will give the glaze a slight sheen and slight caramel note. Use the same volume.