wild mushroom and stilton galette

Make the pastry: Whisk together the flour and salt in a large bowl. Sprinkle bits of butter over dough and using a pastry blender, cut it in until the mixture resembles coarse meal, with the biggest pieces of butter the size of tiny peas. In a small bowl, whisk together the sour cream, lemon juice and water and add this to the butter-flour mixture. With your fingertips or a wooden spoon, mix in the liquid until large lumps form. Pat the lumps into a ball; do not overwork the dough. Cover with plastic wrap and refrigerate for 1 to 2 hours, until very cold.Meanwhile, make the filling: Place the dried mushrooms in a small bowl and add the boiling water. Let stand for 30 minutes until softened. Drain the mushrooms and mince finely.Heat oven to 400°F.In a large sauté pan over medium heat, melt the butter. Add the green onions and sauté, stirring occasionally, until soft, about 5 minutes. Add the garlic, rosemary and thyme and continue to cook, stirring, for 1 minute more. Increase the heat to high, add the fresh and rehydrated mushrooms, season well with salt and pepper, and sauté until the mushrooms are tender and the liquid they released has completely evaporated, 8 to 10 minutes. Transfer to a plate and let cool. On a floured work surface, roll out the dough into a 12-inch round. Transfer to an ungreased baking sheet. Crumble the blue cheese into a bowl, add the cooled mushrooms and stir well. Spread the mixture over the dough, leaving a 1 1/2-inch border. Fold the border over the mushrooms and cheese, pleating the edge to make it fit. The center will be open.If you’d like, brush the outside of the dough with the egg wash for a deeper, shinier color.Bake until golden brown, 30 to 40 minutes. Remove from the oven, let stand for 5 minutes, then slide the galette onto a serving plate. Cut into wedges and serve hot, warm or at room temperature. Do ahead: Galette keeps well in the fridge for 4 to 5 days.