Mushroom and Gruyère Galette

Instructions

1. Prepare the dough
   In a large bowl, whisk together flour and salt. Add the cold butter cubes and use a pastry cutter or your fingers to work the butter into the flour until the mixture resembles coarse meal with some pea-sized pieces. Gradually add ice water, 1 tablespoon at a time, stirring with a fork until the dough just comes together. Form into a disk, wrap in plastic, and refrigerate for at least 1 hour.
2. Sauté the mushrooms
   Heat olive oil in a large skillet over medium heat. Add shallots and cook until softened, about 2 minutes. Add garlic and cook for 30 seconds until fragrant. Add mushrooms and thyme, increase heat to medium-high, and cook until mushrooms release their moisture and begin to brown, about 8-10 minutes. Add balsamic vinegar, scraping up any browned bits from the bottom of the pan. Season with salt and pepper. Remove from heat and let cool completely.
3. Assemble the galette
   Preheat oven to 375°F (190°C). On a floured surface, roll the dough into a 14-inch circle, about 1/8-inch thick. Transfer to a parchment-lined baking sheet. Sprinkle half of the Gruyère cheese over the dough, leaving a 2-inch border. Spread the cooled mushroom mixture evenly over the cheese, then top with remaining Gruyère.
4. Form the crust
   Fold the edges of the dough over the filling, pleating as you go around, leaving the center open. Brush the dough with beaten egg for a golden finish.
5. Bake to perfection
   Bake until the crust is golden brown and the filling is bubbling, about 40-45 minutes. If the crust browns too quickly, cover the edges with foil. Let cool on the baking sheet for 10 minutes before slicing and serving.