- 2 1/2 cups all-purpose flour
- 2 sticks unsalted butter , cut into small pieces
- 1 teaspoon kosher salt
- 1 teaspoon sugar
- 4 to 6 tablespoons ice water
- 1 egg yolk
- 1 tablespoon heavy cream
- 2 tablespoons olive oil
- 1 tablespoon unsalted butter
- 3 large Vidalia onions , thinly sliced
- 1 tablespoon thyme
- 1 to 2 teaspoons black pepper
Meanwhile, in a large sauté pan over medium flame, heat oil and butter. Once hot, add onions; cook slowly until golden brown, about 25 minutes. Stir in thyme, salt, and pepper. Set aside.
Preheat oven to 375°F. Roll out dough on a floured piece of parchment into 14- to 15-inch circle. Place cooled onion mixture in center, fold over edges about 2 inches. In a small bowl, combine egg yolk and heavy cream; brush mixture over edges of dough. Bake until golden brown, 20 to 25 minutes. Serve warm.