Sourdough Caramelized Onion and Kale Flatbread

Name: Sourdough Caramelized Onion and Kale Flatbread
Prep time: 15 min
Cook time: 1 h
Total time: 1 h 15 min
Yield: 4 servings
Cuisine: Mediterranean
Ingredients: 1 lb (450 g) sourdough dough, at room temperature; 3 (700 g) large yellow onions, sliced into ½-inch rings; 5 tbsp (75 ml) olive oil, divided, 2 tbsp for caramelizing, 1 tbsp for stretching, 2 tbsp for finishing; ½ tsp (2½ g) kosher salt; 1 bunch (225 g) fresh Lacinato or curly kale, stems removed, leaves roughly chopped into 2-inch pieces; ½ tsp (1 g) black pepper, freshly ground; ¼ tsp (1 g) fleur de sel or flaky sea salt; 2 (6 g) garlic cloves, minced (optional); ⅛ tsp (½ g) red pepper flakes (optional); 1 tsp (1 g) fresh thyme, leaves only (optional)

From the MyKitchenBank Kitchen

A rustic Mediterranean-style flatbread built on a tangy sourdough base and topped with deeply caramelized sweet onions, tender sautéed kale, and finished with premium olive oil and sea salt. The slow-cooked onions bring rich, complex sweetness that beautifully complements the earthy kale and fermented sourdough flavor.

Prep: 15 min
Cook: 1 hr
Wait: 20 min
Total: 1 hr 35 min
Makes: 1 flatbread (4 slices)

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Steps

Before you start

Remove sourdough dough from the refrigerator 30 minutes ahead to bring it to room temperature
Preheat your oven 15 minutes before topping and baking the flatbread
Slice and prepare all ingredients before you start caramelizing the onions
Use a large, heavy-bottomed skillet (12 inches) for even caramelization of the onions

1
Caramelize the onions
- Heat 2 tbsp of the olive oil in a large skillet over medium-low heat.
- Add the sliced onions and ½ tsp kosher salt, stirring well to coat.
- Cook, stirring every 3–4 minutes, for 40–45 minutes total.
- The onions will gradually turn golden, then deep golden-brown with caramelized edges, becoming glossy and reduced in volume by about 75%.
- You'll notice a rich, sweet aroma when they're done.
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Ready when: Deep golden-brown color, glossy and syrupy appearance, volume reduced to about 25% of original, sweet aroma
Tip: If the pan begins to dry out, add 2 tbsp water to help release the onions' natural moisture. Avoid the temptation to turn up the heat—true caramelization is a slow, patient process that cannot be rushed without sacrificing flavor.
2
Prepare the kale
- While the onions caramelize, remove the tough center ribs from the kale leaves by folding each leaf in half and slicing along the rib.
- Discard the ribs.
- Roughly chop the remaining leaves into 2-inch pieces and set aside.
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Tip: Do this while the onions cook to save time and keep your workspace organized.
3
Shape the dough and start preheating ovenOven 475°F / 245°C
- About 20 minutes into the onion cooking, place the sourdough dough on a parchment-lined baking sheet or lightly oiled pizza pan (roughly 14 inches).
- Gently stretch the dough to fit the pan, aiming for a thickness of ¼ to ½ inch.
- Let the dough rest for 15 minutes while you finish the onions and the oven preheats.
- Preheat your oven to 475°F (245°C) during this rest period.
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Tip: Sourdough dough can be elastic; if it springs back significantly while stretching, let it rest a few minutes and gently stretch again. This prevents a tough, overstretched final crust.
4
Sauté the kale with caramelized onions
- Once the onions are deeply caramelized (at about the 40–45 minute mark), add the chopped kale to the skillet and stir well to combine.
- Cook over medium heat for 3–4 minutes, stirring occasionally, until the kale is wilted and tender.
- If using garlic, add it now and cook for 1 minute more until fragrant.
- Season with ½ tsp black pepper.
- Taste and adjust salt if needed.
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Ready when: Kale is wilted and dark green, tender when bitten, combined with the onions
Tip: The residual heat and oil from the caramelized onions will quickly soften the kale without making it mushy. Don't overcook at this stage—the kale will continue to soften slightly during baking.
5
Top and bake the flatbreadOven 475°F / 245°C
- Lightly brush the rested dough with 1 tbsp of the olive oil.
- Spread the caramelized onion and kale mixture evenly over the dough, leaving a ½-inch border around the edges.
- Sprinkle with ¼ tsp fleur de sel and ⅛ tsp red pepper flakes (if using), and scatter the fresh thyme leaves over the top (if using).
- Carefully transfer the baking sheet to the preheated 475°F oven and bake for 18–20 minutes, until the edges are golden brown and crispy.
- Check the bottom by carefully lifting an edge with a thin spatula—it should be evenly browned, not pale.
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Ready when: Edges are golden brown, bottom is crispy and evenly browned when lifted, flatbread sounds hollow when tapped
Tip: If your oven runs hot, begin checking at 16 minutes. If it runs cool, it may need up to 22 minutes. Every oven is different, so trust your eyes and the bottom-crust test.
6
Rest and finish
- Remove the flatbread from the oven and immediately drizzle with 1–2 tbsp of good-quality finishing olive oil, which will add a peppery or fruity note as it pools into the still-warm flatbread.
- Let cool for 5 minutes to allow the cheese and toppings to set slightly and to make slicing easier without burning your mouth.
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Tip: Save your best olive oil for this finishing step—its flavor will shine when drizzled over the warm flatbread. A robust extra-virgin or a garlicky variety both work beautifully.

Good to know

Tips

Don't rush the onion caramelization. Low heat and patient stirring every few minutes yield sweet, complex flavor. High heat browns the surface but won't develop the depth and caramel notes you're after.
For a cheese variation, scatter ½ cup (60 g) grated Gruyère or Pecorino Romano over the toppings before baking. The cheese will melt into pockets and add richness without overpowering the onions and kale.
This flatbread is equally delicious warm, at room temperature, or even cold the next day, making it perfect for picnics, lunch boxes, or casual entertaining.
If the dough has been refrigerated, it may be stiff and cold. Leaving it on the counter for 30 minutes softens it and makes stretching much easier without tearing.

Make ahead

The sourdough dough can be made 1–2 days ahead and stored in the refrigerator, or purchased from a local bakery. The caramelized onions and kale can be made up to 4 hours ahead; gently reheat them in the skillet over low heat before topping the dough.

Storage & reheating

Store leftover flatbread covered at room temperature for up to 2 days (though best enjoyed the same day). Refrigerate in an airtight container for up to 4 days. Reheat in a 350°F oven for 10–12 minutes until warmed through. Freeze wrapped tightly in plastic wrap and foil for up to 3 months; thaw overnight in the refrigerator and reheat as above.

Substitutions

fresh Lacinato or curly kale → Fresh spinach, Swiss chard, or arugula. Spinach and chard will wilt in 1–2 minutes instead of 3–4. For a peppery finish, add raw arugula after baking rather than wilting it with the onions.
sourdough dough → Store-bought pizza dough, whole wheat dough, or puff pastry. Pizza dough will bake faster (14–16 minutes) and puff pastry will rise dramatically. Adjust baking time and watch the bottom carefully.
large yellow onions → Red onions or shallots. Red onions add a mild sweetness; use the same quantity. Shallots caramelize faster (25–30 minutes), so watch closely and stir more frequently.
kosher salt → Fine sea salt. Fine sea salt is denser, so reduce to ⅜ tsp (about 2 g) to avoid over-salting.