- 2 cups all-purpose flour
- 1 teaspoon kosher salt
- 1 teaspoon sugar
- 8 tablespoons cold unsalted butter, cut into pieces
- 1/4 cup ice water
- 2 Yukon gold potatoes, thinly sliced
- 1 tablespoon olive oil
- 4 pancetta, cubed
- 3 medium leeks, white and pale green parts only, halved lengthwise
- 3/4 cup mascarpone or crème fraîche
- 1/2 cup gruyere or comte, grated
- 1 teaspoon thyme leaves, plus extra for garnish
- 1 large egg, beaten with 2 tablespoons water
- In a large bowl, mix together flour, salt, and sugar. Add chilled butter pieces into the bowl. Working quickly, use your fingers to run butter pieces into the flour to create large, scraggly pieces of dough. (The idea is to create different sized clumps and strands of butter to achieve a flaky crust.)
- Evenly drizzle ice water over the dough, and with your fingers, bring the dough together. Note: The dough will look a little dry. Turn the dough out onto a work surface and knead 2-3 times until the saggy edges come together. Flatten dough to form a 1-inch thick disk, then wrap in plastic wrap. Set in the fridge for at least 30 minutes or overnight. (Dough can be made up to 5 days ahead, chilled; or kept in the freezer for up to 1 month.)
- When ready to assemble, preheat oven to 400 degrees.
- In a medium skillet, heat olive oil over medium heat. Add pancetta and cook for 5-6 minutes. Remove pancetta from skillet with a slotted spoon but leave excess fat to remain in pan. Add leeks, cut side down, and cook for 5-7 minutes, until they become slightly golden. Remove from heat.
- On a lightly floured surface, roll dough into a 12-inch circle. Transfer to a parchment paper-lined baking sheet.
- Spread mascarpone over dough, leaving a 1-inch border. Scatter 3/4 of the gruyere and 1/2 of the pancetta over the mascarpone.
- Evenly layer sliced potatoes over top, then add thyme leaves. Season with salt and pepper. Add the leeks, cut side up and sprinkle remaining cheese and pancetta over top. Fold edges of dough over the filling. Brush crust with egg wash.
- Bake galette for 35-45 minutes until the crust is golden and flaky, and the potatoes have softened. Let cool slightly then top with extra thyme leaves.