Mushroom and Leek Gallette

In a food processor, combine the flour, butter, and a pinch of salt. Pulse until the mixture resembles coarse crumbs. Slowly add the cold water while pulsing, until the dough comes together. Shape the dough into a disk, wrap in plastic wrap, and refrigerate for 30 minutes.

Preheat the oven to 400°F (200°C).

In a large skillet, heat the olive oil over medium heat. Add the leeks and cook until softened, about 5 minutes. Add the mushrooms, garlic, thyme, salt, and black pepper. Cook for another 5 minutes, until the mushrooms are tender.

On a floured surface, roll out the dough into a circle about 12 inches in diameter. Transfer the dough to a baking sheet lined with parchment paper.

Sprinkle half of the grated Gruyere cheese onto the center of the dough, leaving a 2-inch border. Spoon the mushroom and leek mixture over the cheese. Fold the edges of the dough over the filling, pleating as necessary.

Brush the beaten egg over the edges of the dough. Sprinkle the remaining grated Gruyere cheese over the filling.

Bake for 25-30 minutes, until the crust is golden brown. Let the gallette cool for 10 minutes before serving.