CARAMELIZED ONION TART RECIPES

Steps:

• Prepare the dough: In a large bowl, whisk together flour, sugar, 1 1/2 teaspoons kosher salt and 1 1/2 teaspoons black pepper. Add butter and 1 cup grated Gruyère to the flour mixture and toss to coat. Using your fingertips, pinch the butter and cheese into the flour to make pebble-size pieces. Drizzle in the ice water and stir to make a shaggy dough. Dump the dough onto a large sheet of plastic wrap and knead a few times to combine. Wrap in plastic and refrigerate for at least 4 hours.
• Prepare the onions: In a large skillet, melt the butter over medium-high heat. Add onions and thyme sprigs, season with 1 teaspoon salt and 1/2 teaspoon pepper and cook, stirring occasionally, until the onions are translucent and lightly golden on the edges, 20 to 25 minutes. Reduce the heat to medium, add broth and sherry and cook until the onions are browned and the liquid has mostly evaporated but the mixture is still saucy, 16 to 18 minutes. Transfer to a bowl and set aside to cool for at least 30 minutes.
• Heat the oven to 375 degrees. Roll the dough into a 13-inch round on a sheet of parchment. Spread the cooled caramelized onions on the dough, leaving a 1- to 2-inch border. Fold the edges in, over the onions, transfer to a baking sheet and bake until the dough is golden brown and some of the onions have browned on the edges, 40 to 50 minutes, rotating the galette halfway into the baking process.
• Remove galette from the oven and sprinkle remaining 1/3 cup grated Gruyère on the crust. Bake another 5 minutes to melt the cheese. Remove and let rest for 10 minutes before slicing. Top with remaining thyme leaves, for garnish.

Steps:

• Whisk whole wheat flour, salt, and 1 cup all-purpose flour in a large bowl to combine. Add butter and work into dry ingredients with your fingers, smashing between your palms to flatten, until largest pieces are the size of a nickel. Drizzle in 6 Tbsp. ice water and rake in with your fingers. Gently squeeze handfuls of mixture together until a shaggy dough forms. Turn out onto a work surface and knead until only a few dry spots remain. Pat into a disk and wrap in plastic. Chill until very firm, at least 2 hours or up to 3 days.
• Roll out dough on a lightly floured surface to about ?" thick. Transfer to tart pan. Lift up edges and allow dough to slump down into pan. Gently press into corners and trim excess. (If using springform pan, trim dough to 1½" up sides of pan). Freeze until firm, 15–20 minutes, or cover and chill up to 12 hours.
• Place a rack in lower third of oven; preheat to 350°. Swirl 2 Tbsp. oil in a large skillet to coat bottom and add yellow onions; season with kosher salt. Set skillet over medium heat and cook onions, stirring occasionally and making sure to scrape bottom of pan, until very soft and deep golden brown, 15–20 minutes. Add garlic and cook, stirring occasionally, until onions are caramelized and deeply browned, 25–30 minutes (if any pieces get super dark and stick to the pan, a few drops of water should dislodge them). Let cool.
• Brush mustard over chilled dough, then sprinkle with cayenne. Stir cheese into caramelized onion mixture and spread across crust in an even layer.
• Using a mandoline or very sharp knife, thinly slice both squashes crosswise. Cut sweet potato and red onion in half lengthwise, then thinly slice crosswise with mandoline. Arrange vegetables in concentric circles, with rounded edges facing up, starting from the outside edge, leaning slices against the crust, and working your way inward. Drizzle remaining 2 Tbsp. oil over vegetables and season with kosher salt.
• Bake tart until edges of vegetables are browned (a few spots may even get deeply browned) and crust is golden brown, 75–90 minutes.
• Melt thyme and butter in a small saucepan and cook just until butter is bubbling. Brush over tart with a pastry brush and sprinkle with sea salt.