French Gâteau aux Myrtilles (Blueberry Cake with Crème Mousseline)
An elegant French layer cake featuring a delicate almond sponge cake filled with silky crème mousseline (a rich pastry cream lightened with whipped butter) and studded with fresh blueberries. The contrast of the tender crumb, velvety cream, and tart-sweet berries creates a sophisticated dessert perfect for special occasions. This recipe yields a 7-inch cake serving 8–10 people.
- Prep
- 45 min
- Cook
- 30 min
- Wait
- 1 hr 45 min
- Total
- 3 hr
- Makes
- One 7-inch (18 cm) layer cake, 8–10 servings
Steps
Before you start
- Bring eggs and butter to room temperature (at least 1 hour ahead).
- Preheat oven to 350°F (175°C).
- Butter and line the bottoms of two 7-inch (18 cm) cake pans with parchment paper.
- Sift almond flour and cake flour together before using to remove lumps.
Combine dry ingredients for cake
- In a medium bowl, whisk together the sifted cake flour, almond flour, baking powder, and fine sea salt.
- Set aside.
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Ready when: Dry ingredients are well combined and no lumps remain.
Tip: Sifting removes lumps from the almond flour and ensures an even, tender crumb.
Whip egg whites to stiff peaks
- In a large, impeccably clean bowl, whip the 5 egg whites with an electric mixer on medium-high speed until stiff, glossy peaks form, 3–4 minutes.
- Set aside.
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Ready when: Whites form stiff, glossy peaks and do not slide when the bowl is tilted.
Tip: Even a tiny drop of fat will prevent the whites from reaching full volume; use a very clean bowl and beaters.
Cream yolks with sugar
- In another large bowl, whisk the 6 egg yolks (5 from the separation plus 1 extra) and granulated sugar together by hand or with an electric mixer on medium speed for 2–3 minutes until the mixture is pale, thick, and falls in ribbons from the whisk.
- This aeration is crucial for a light cake.
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Ready when: Mixture is pale, thick, and ribbony when the whisk is lifted.
Tip: Don't rush this step; proper aeration creates a fine, tender cake crumb.
Fold dry ingredients into yolks
- Gently fold the dry flour mixture into the egg yolk mixture using a rubber spatula, folding just until no streaks of flour remain.
- Do not overmix.
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Ready when: No visible flour streaks remain in the batter.
Tip: Use a folding motion, not stirring, to preserve the aeration from the egg yolks.
Fold in butter and add whites
- Pour the melted butter and vanilla extract over the batter, then fold to combine.
- Now gently fold in the whipped egg whites in two additions, folding just until combined and no white streaks remain.
- The batter should be light and airy.
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Ready when: No visible egg white streaks remain; batter is uniform and mousse-like.
Tip: Overfold here and you'll deflate the whites. Fold gently until just combined, not until perfectly smooth.
Divide batter and add milk to half
- Divide the batter in half.
- Gently fold the milk into one half to loosen it slightly; this portion will be the bottom layer.
- Leave the other half thick and voluminous for the top layer.
- Pour the milky batter into one prepared 7-inch pan and the thicker batter into the other.
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Ready when: Batter is evenly distributed in both pans.
Tip: The difference in thickness helps both layers bake at the right rate for optimal texture.
Bake cake layersOven 350°F / 175°C
- Bake both pans in a preheated 350°F (175°C) oven for 25–30 minutes.
- The cakes are done when a wooden toothpick inserted into the center comes out clean and the tops are light golden and spring back when lightly pressed.
- Do not overbake or the cake will be dry.
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Ready when: Toothpick comes out clean, tops are light golden, and cake springs back when pressed.
Tip: If the tops brown too quickly, tent with foil for the last 5–10 minutes. Overbaking is the enemy of tender cake.
Cool cakes
- Remove the pans from the oven and let cool in the pans for 10 minutes.
- Then turn the cakes out onto a wire rack and cool completely to room temperature, about 45 minutes.
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Ready when: Cakes are cool to the touch and stable.
Tip: Do not assemble the cake until it is fully cooled, or the mousseline will melt.
Infuse milk with vanilla
- Pour the whole milk into a medium saucepan.
- Split the vanilla bean lengthwise and scrape the seeds into the milk, then add the scraped pod as well.
- Heat over medium heat, stirring occasionally, until it reaches a gentle simmer.
- Remove from heat and let steep for 10 minutes to extract maximum flavor, then remove and discard the pod.
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Ready when: Milk reaches a gentle simmer; vanilla bean pod is removed after steeping.
Tip: Infusing the milk with fresh vanilla bean gives a superior, more elegant flavor than extract alone.
Prepare pastry cream base
- In a medium bowl, whisk together the 4 egg yolks and 65 g (⅓ cup) granulated sugar until pale and thick, about 2 minutes.
- Whisk in the cornstarch and fine sea salt until no lumps remain.
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Ready when: Mixture is pale and thick; cornstarch is fully incorporated with no lumps.
Tip: Whisking the cornstarch with the egg yolks prevents lumping when the hot milk is added.
Cook pastry creamOven 175°F / 80°C
- Slowly pour the hot vanilla-infused milk into the egg yolk mixture while whisking constantly to prevent the yolks from scrambling.
- Once combined, pour the mixture back into the saucepan and heat over medium heat, stirring constantly with a rubber spatula, until it reaches 175°F (79°C) on an instant-read thermometer and is thick enough to coat the back of the spatula (approximately 3–4 minutes).
- The cream should boil gently for at least 1 minute to ensure the cornstarch is fully set.
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Ready when: Cream reaches 175°F (79°C) and coats the back of the spatula; it boils gently for at least 1 minute.
Tip: Reach 175°F to ensure food safety and full thickening of the cornstarch. Constant stirring prevents lumps and scorching.
Strain and cool pastry cream
- Press the pastry cream through a fine-mesh strainer into a clean bowl to remove any lumps or cooked bits of egg.
- Press plastic wrap directly onto the surface to prevent a skin from forming.
- Chill in the refrigerator until cool to the touch, about 15–20 minutes.
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Ready when: Pastry cream is smooth, strained, and cool to the touch.
Tip: The plastic wrap prevents oxidation and skin formation, keeping the cream silky.
Make crème mousseline
- In a large bowl, beat the 140 g (5 oz) cold, cubed butter with an electric mixer on medium-high speed for 2–3 minutes until it becomes light, fluffy, and pale, like whipped cream.
- Reduce the speed to medium and gradually add the cooled pastry cream in 4–5 additions, beating well after each addition until completely incorporated.
- The mousseline should be silky, light, and mousse-like.
- If it looks separated or broken, continue beating; it will come together.
- Chill for 30 minutes before using.
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Ready when: Mousseline is light, fluffy, and mousse-like; it holds a peak.
Tip: Add the pastry cream gradually; rushing causes a broken or greasy texture. If it breaks, beat longer—it will emulsify. Cold ingredients are essential.
Assemble the cake
- Level the tops of both cooled cake layers with a serrated knife if needed.
- Place the thicker cake layer on a cake plate or serving board.
- Spread or pipe about one-third of the chilled crème mousseline onto the first layer.
- Scatter half of the blueberries evenly over the mousseline.
- Place the second cake layer on top and spread or pipe the remaining mousseline over the top and sides.
- Arrange the remaining blueberries artfully on top of the cake.
- Dust lightly with powdered sugar if desired.
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Ready when: Cake is assembled with mousseline and blueberries arranged, ready to serve.
Tip: Work quickly so the mousseline doesn't warm and soften. Chill the assembled cake for 30 minutes before serving for clean slices.
Chill and serve
- Refrigerate the assembled cake for at least 30 minutes (up to 4 hours) before serving.
- This allows the mousseline to set and makes the cake easier to slice.
- Slice with a hot, wet knife, wiping it clean between cuts.
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Ready when: Cake is chilled and firm, ready to slice cleanly.
Tip: A hot, wet knife ensures clean cuts through the delicate layers and prevents the mousseline from sticking.
Good to know
Tips
- The success of crème mousseline depends on cold butter and proper emulsification: add the pastry cream slowly and beat well between additions. If it breaks (looks curdled), continue beating—it will come together.
- For a showier presentation, reserve some crème mousseline and pipe rosettes around the top edge of the cake before arranging blueberries in the center.
- This is a professional-level technique: take your time with each step, especially whisking the egg whites and folding. Aeration is everything in this cake.
- Toast the almond flour lightly in a dry skillet over low heat for 2–3 minutes before using (cool completely) to intensify the almond flavor, if desired. Omit the milk step when doing this to prevent oversaturation.
Storage & reheating
Store the assembled cake covered in the refrigerator for up to 2 days. The unfrosted cooled cake layers may be wrapped individually in plastic wrap and frozen for up to 1 month; thaw at room temperature before assembly. Crème mousseline can be made up to 1 day ahead and kept chilled. Do not freeze the assembled cake, as the texture of the mousseline will suffer.
Substitutions
- vanilla bean, split lengthwise → 1 tsp vanilla extract. Vanilla extract is less aromatic but convenient. Stir it in after the milk is cooled rather than infusing it.
- fresh blueberries → raspberries, blackberries, or mixed berries, rinsed and patted dry. Other berries will work beautifully. Use the same weight and adjust quantities to fit. Avoid strawberries, as they don't hold up as well in the mousseline.
- almond flour (finely ground) → 75 g (¾ cup) finely ground hazelnuts or pistachios. These will shift the flavor slightly but create a delicious variation. Keep the weight and total flour ratio the same.
- cornstarch → 2 tbsp arrowroot powder. Arrowroot gives a slightly more delicate texture. Use the same amount and adjust cooking time slightly if needed.
