Here’s one of my favorite savory tarts, an enticing combination of sweet caramelized onions, fresh thyme and nutty Gruyere cheese, baked together in a tender whole wheat pastry crust. I love this on a cold winter day, right out of the oven, but it’s also great at room temperature on a warm day, served with a light salad. I also make mini-versions of this to serve as hors d’oeuvres, which are always a hit. If you can’t find Gruyere cheese, Emmental and Jarlsberg are good substitutes, and you can use Vidalia onions in place of the yellow onions, if you like.
Makes one 11-inch tart, serving 8
Whole Wheat Crust:
- 1 cup (130 grams) all-purpose flour
- 1/3 cup (41 grams) whole wheat flour
- ¼ teaspoon fine sea salt
- 8 tablespoons (113 grams) unsalted butter, cut into 1/2-inch cubes and frozen for 15 minutes
- ¼ cup (56 grams) ice-cold water
- 4 tablespoons (56 grams) unsalted butter, cut into 4 pieces
- 2 pounds (907 grams) yellow onions, peeled, cut in half lengthwise, and thinly sliced
- Fine sea salt, as needed
- Water, as needed
- Freshly ground pepper
- 2 large 100 grams) eggs
- 1/3 cup (77 grams) heavy cream
- 1/3 cup (80 grams) whole milk
- 1 teaspoon fresh thyme leaves, chopped
- 1/8 teaspoon fine sea salt
- A few grinds of freshly ground black pepper
- 3 ounces (85 grams) Gruyere cheese, grated (about 1 1/3 cups grated)
Make the crust:
- Place the all-purpose and whole wheat flours and the salt in the bowl of a food processor and pulse to combine. Scatter the frozen butter cubes on top of the flour and pulse the machine just until the mixture resembles coarse crumbs. Add the cold water and pulse until the dough starts to come together.
- Transfer the dough to a work surface and shape it into a disc. Wrap the dough in plastic wrap and refrigerate until ready to use (or at least 1 hour).
Make the caramelized onions:
- In a large skillet, melt the butter over medium-low heat. Add the sliced onions and a big pinch of salt and cook, covered, until the onions have softened, about 10 minutes. Remove the cover and continue to cook the onions, stirring occasionally, until they are nicely browned and lightly caramelized, 30 to 45 minutes. As they cook, add a tablespoon of water anytime the onions begin to stick to the bottom of the pan and are in danger of burning. Remove the pan from the heat and season with more salt and pepper as needed. Let the onions cool completely. (The onions can be caramelized up to 3 days in advance, or up to a month, if you want to freeze them.)
Roll out and bake the crust:
- Place the tart dough on a lightly floured work surface and, using a rolling pin, roll it out to a 13-inch round. Roll the circle up on the rolling pin and unroll it onto an 11-inch tart pan with a removable bottom. Press the dough into the bottom and sides of the pan, then trim off any excess dough. Using a fork, prick the bottom of the tart shell all over at 1-inch intervals. Refrigerate the tart shell for 30 minutes. Meanwhile, position a rack in the center of the oven and preheat the oven to 400˚F.
- Cover the tart pan with a piece of parchment paper and then fill it with pie weights, dried beans or uncooked rice. Place the tart pan on a baking sheet and bake for 20 minutes, until the crust is set. Carefully remove the parchment paper and pie weights, then return the tart shell to the oven and bake for another 12 to 15 minutes, until the crust is lightly browned. Cool the tart shell in the pan, set on a wire rack, for 15 minutes. Reduce the oven temperature to 375˚F.
Assemble and bake the tart:
- Spread the caramelized onions over the bottom of the tart shell in an even layer.
- In a medium bowl, whisk the eggs together until blended. Whisk in the cream, milk, thyme leaves, salt and pepper. Place the tart pan and crust on a baking sheet and carefully pour the filling into the crust. Sprinkle over the cheese. Bake the tart for 25 to 35 minutes, or until the filling is set and golden brown. Transfer the tart pan to a wire rack and cool before serving.