Savory Potato and Onion Galette

1.In a large bowl, combine the flour, salt, and black pepper. Add the cubed cold butter and use a pastry cutter or your fingers to work it into the flour until the mixture resembles coarse crumbs.

2.Gradually add the cold water, one tablespoon at a time, mixing until the dough comes together. Shape the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 30 minutes.

3.While the dough is chilling, heat olive oil in a large skillet over medium heat. Add the sliced onions and cook, stirring occasionally, until they are caramelized and golden brown, about 15-20 minutes. Add the thyme and stir to combine. Remove from heat and let cool slightly.

4.In the same skillet, add the sliced potatoes and cook for about 5-7 minutes, just until slightly tender. Season with salt and pepper.

5.Preheat your oven to 400°F (200°C).

6.On a lightly floured surface, roll out the chilled dough into a large circle, about 1/8 inch thick. Transfer the dough to a parchment-lined baking sheet.

7.Spread the caramelized onions evenly over the dough, leaving a 2-inch border around the edges. Layer the sliced potatoes on top of the onions, and sprinkle with Gruyère cheese if using.

8.Fold the edges of the dough over the filling, pleating it as you go to create a rustic look. Brush the edges with the beaten egg to give it a golden color when baked.

9.Bake in the preheated oven for 30-35 minutes, or until the crust is golden brown and the potatoes are tender.

10.Allow the galette to cool for a few minutes before slicing and serving warm.