A sort of a cross between a tart and a quiche, this tart uses a French pie dough and a mushroomy, eggy filling. You can use any kind of fresh mushrooms and you can use store-bought pie dough if you want.
Mix together the flour, salt and sugar into the bowl of a food processor. Add half the butter and pulse 5-7 times to cut it into the flour. Do this with the other half of the butter. Keep pulsing it until the dough starts to look like cornmeal. You can also do all this by hand in a large bowl.
Add the ice water and the vinegar and pulse a few more times. Turn the dough out onto a clean surface and work it into a ball. You don't really want to knead it much or the crust will be tough. Wrap the dough in plastic and set it in the freezer if you are moving right to making the filling, or in the fridge if you're going to wait. You can keep the dough in the fridge a few days.
FILLING
Cook the bacon in a large sauté pan until crispy. Eat a piece, then chop the rest roughly and set aside.
While the bacon is cooking, chop most of your mushrooms, leaving some nice pretty ones as decoration, or, if they are large, make pretty cross-section slices to decorate the tart.
Sauté the onions in the bacon fat for a minute or three, then add the mushrooms. Turn the heat up to high and cook until you are getting a little browning on the onions and mushrooms, about 8 minutes or so. Turn off the heat and let this cool.
MAKING THE TART
When you are ready to make the tart, preheat the oven to 425°F. Roll out the dough on a clean, floured surface until it's about 1/4-inch thick. Lay it over the tart pan and use your fingers to set it snugly into the fluted edges and corners of the pan. Run a rolling pin over the top edges of the pan to cut the dough cleanly off.
Add the beaten eggs, sour cream, parsley and grated cheese to the filling mix and stir well. Fill the tart. You'll want to set the tart on a baking sheet in the oven -- this makes it easier to remove later without inadvertently popping the bottom out. Bake uncovered for 15 minutes.
Drop the heat to 350°F and keep baking until the top is pretty and browned. Remove the baking sheet with the tart on it and let this cool 5 minutes before popping the tart out of its pan. Serve warm or at room temperature.
Notes
If you want to make this vegetarian, use 3 tablespoons butter instead of the bacon.