1 large butternut squash, peeled, seeded, and cubed
1 tablespoon olive oil
2 large yellow onions, halved and sliced
3 tablespoons unsalted butter
2 eggs
8 ounces crème fraîche
4 ounces Gruyère, grated
2 ounces Parmesan, grated
1 teaspoon sea salt
1 teaspoon freshly ground black pepper
4sprigs thyme
Melt butter in large saucepan over medium heat. Add onions, thyme sprigs, and 1/2 teaspoon salt, stirring to mix. Cover and reduce heat to low. Cook, stirring occasionally, until dark golden brown, about 45 minutes. Remove thyme stems.
Meanwhile, preheat oven to 450° F. Toss butternut squash with olive oil and 1/2 teaspoon salt and spread out on baking sheet. Bake until browned and very soft, stirring once, about 40 minutes.
Reduce oven heat to 350° F. Roll dough out until thin and press into a well-greased 10-inch tart pan. Prick all over with a fork and bake in oven 10 minutes.
In a medium mixing bowl, combine eggs, crème fraîche, gruyère, Parmesan, and black pepper.
Spread caramelized onions in bottom of tart and top with butternut squash. Pour gruyère mixture over the squash, making sure to spread it evenly throughout the tart.
Bake until golden brown and cooked through, about 30 to 40 minutes.
Pastry Dough
3/4 cup all-purpose flour
1/2 cup whole wheat flour
1/4 teaspoon salt
1 stick butter
4 tablespoons ice water
Cut butter into 1-tablespoon pieces and freeze for 10 minutes.
Mix flour and salt in food processor or large bowl.
If using food processor, add butter and mix until mixture resembles small pea-sized balls. If mixing by hand, work quickly, mixing the butter in with your hands until it forms small pea-sized balls.
Add in ice water and mix just until dough forms and comes together. Form into disk, wrap in plastic, and place in fridge for 20 minutes.
1 recipe pastry dough (see below)