Step 1

Melt butter in a large skillet over medium heat. Add leeks, thyme, and 1/3 cup water. Season with salt and pepper. Cook, stirring frequently, until leeks are tender, 12 to 14 minutes.

Step 2

Add wine and cook until thickened, 2 to 3 minutes. Add cream and cook until it begins to coat leeks, 1 to 2 minutes. Season with salt and pepper. Cool slightly.

Step 3

Preheat oven to 400°F. Line a rimmed baking sheet with parchment paper. Allow dough to rest on the work surface for 5 minutes. On a lightly floured work surface, roll dough to a 13-inch circle; transfer to prepared pan. Top with Gruyère, then leek mixture, leaving a 2- to 3-inch border all around. Fold edges of dough around the filling, overlapping and pressing gently to seal. Brush dough with cream. Bake until crust is golden brown, 30 to 35 minutes. Serve warm or at room temperature.