Mushroom and Leak Galette Sunday Dinner

adapted from Smitten Kitchen

For the pastry:
1 1/4 cups all-purpose flour
1/4 teaspoon salt
8 tablespoons (1 stick) unsalted butter, cut into
pieces
1/4 cup sour cream
2 teaspoons fresh lemon juice
1/4 cup ice water

For the filling:
2 leeks washed and chopped

1 1/2 cups of sliced mushrooms
2 tablespoons olive oil
1 to 2 tablespoons butter (if you have only non-stick, the smaller amount will do)
1 teaspoon salt and pepper to taste
3/4 cup fontina cheese (about 2 1/2 ounces), grated or cut into small bits
1 1/2 teaspoons chopped fresh sage leaves or you can use the leaves from one sprig of thyme. egg wash: 1 egg and a splash of milk or water.

Make the pastry: In a bowl, combine the flour and salt. Place the butter in another bowl. Place both bowls in the freezer for 1 hour. Remove the bowls from the freezer and make a well in the center of the flour. Add the butter to the well and, using a pastry blender, cut it in until the mixture resembles a coarse meal. Make another well in the center. In a small bowl, whisk together the sour cream, lemon juice, and water and add half of this mixture to the well. With your fingertips, mix in the liquid until large lumps form. Remove the large lumps and repeat with the remaining liquid and flour-butter mixture. Pat the lumps into a ball; do not overwork the dough. Cover with plastic wrap and refrigerate for 1 hour. In a saute pan add butter and olive oil then add leek and mushrooms along with herb of choice until all vegetables are cooked.  Add salt and pepper, On a floured work surface, roll the dough out into a 12-inch round. Transfer to an ungreased baking sheet. Spread the leeks and mushrooms mixture over the dough and add the cheese, leaving a 1 1/2-inch border. Fold the border over the top in a pleating fashion leaving the center open. With a pastry brush cover the dough in an egg wash. Bake in a 400 degree pre-heated oven for 30-40 minutes until the galette is cooked a lovely golden brown. Enjoy!