Multicolored Squash Tart with Caramelized Onion
A grain-free walnut crust topped with caramelized onion, cheddar, and concentric squash and sweet potato slices
Serves 6–8 · 1 hr active · 2 hr total · winter (year-round) · early evening
Ingredients
Walnut crust
1 cup raw walnuts
1 cup blanched almond flour
1 large pasture-raised egg
2 tbsp coconut oil or grass-fed butter
½ tsp sea salt
¼ tsp freshly ground black pepper
Caramelized onion base
4 medium yellow onions, thinly sliced
3 garlic cloves, thinly sliced
4 tbsp extra virgin olive oil, divided
pinch Himalayan pink salt
Mustard layer
2 tbsp Dijon mustard
pinch cayenne pepper
Cheese
4 oz coarsely grated sharp raw cheddar (or Gruyère, fontina, or dairy-free cheddar)
Squash and root vegetables
½ small butternut squash (lengthwise half, about 1 ¼ lb), seeds removed
1 delicata squash (about 1 lb), halved lengthwise, seeds removed
1 small sweet potato
1 small red onion
2 sprigs fresh thyme
2 tbsp grass-fed butter, melted
flaky sea salt and freshly ground black pepper
Method
Make the crust. Place the walnuts and almond flour in a food processor. Pulse until the walnuts are finely chopped (still some texture).
Add the egg, coconut oil, salt, and pepper. Pulse until the mixture comes together as a dough.
Press evenly into an 11- or 12-inch fluted tart pan with removable bottom (or 9-inch springform).
Freeze the crust 15–20 minutes.
Bake at 350°F (175°C) for 8–10 minutes, until set but not browned.
Caramelize the onions. Heat 2 tbsp olive oil in a large skillet. Add the yellow onions and a pinch of salt.
Cook over medium heat 15–20 minutes, stirring occasionally, until very soft and golden brown.
Add the garlic. Continue to cook 25–30 minutes more, stirring occasionally, until the onions are deeply caramelized. If any pieces stick to the pan, a few drops of water can dislodge them.
Roast the vegetables (separately). Preheat the oven to 400°F.
Using a mandoline or sharp knife, thinly slice both squashes crosswise. Cut the sweet potato and red onion in half lengthwise, then thinly slice crosswise. All slices should be about ⅛-inch thick.
Toss the vegetable slices with 2 tbsp olive oil, salt, and pepper on a parchment-lined baking sheet.
Roast 25–30 minutes, until tender and lightly caramelized at the edges.
Assemble the tart. Place the par-baked crust on a baking sheet.
Brush the crust with mustard. Sprinkle with cayenne.
Stir the grated cheese into the caramelized onion mixture. Spread evenly across the crust.
Arrange the roasted vegetable slices in concentric circles, with rounded edges facing up. Start at the outside edge, leaning the slices against the crust, and work inward.
Drizzle with remaining 2 tbsp melted butter. Season with flaky sea salt.
Add fresh thyme sprigs across the top.
Bake at 350°F for 30–40 minutes, until the edges of the vegetables are nicely browned (a few spots may even get deeply browned).
Remove and let cool 5 minutes. Sprinkle with additional flaky sea salt before serving.
Nourishment Notes
The concentric-circle arrangement of vegetable slices is the visual signature of this tart, and it's borrowed directly from French galette de légumes tradition. Arranging vegetables in patterns rather than scattering them is the small detail that elevates a rustic preparation to a centerpiece dish — the same principle drives French Provençal tian preparations, where layered vegetables are baked together in a dish. The mandoline is the right tool for getting consistent ⅛-inch slices.
The caramelized onion base is the structural anchor of the dish. Thirty minutes of slow caramelization concentrates the natural sugars in the onion, producing a deep, jammy texture that the palate reads as a sweet contrast to the savory squash and cheese. Skipping or rushing this step produces flat, sharp onions that read as a different ingredient entirely. The same technique drives French onion soup, pissaladière (Provençal onion-and-anchovy tart), and the great Italian focaccia di cipolle.
Delicata squash is the unsung hero of this tart. Unlike most winter squash, delicata has thin, edible skin (no peeling required) and a sweet, custardy flesh that holds its shape when sliced thin. The variety appeared in the late 19th century in the United States, briefly disappeared from commercial cultivation, and returned in the 1990s through farmer's market revival. Its half-moon-shaped slices with the green-and-yellow-striped skin pattern produce particularly beautiful visual contrast in this layered tart.
Storage: Refrigerator up to 4 days. Reheat at 300°F for 12 minutes.
Recipe credit: Adapted from Bon Appétit.