In a mixing bowl, combine the flour, baking powder and salt. Add the cold butter. You can cut it into small pieces, or you can use a grater and grate it like I do. Rub the butter into the dry ingredients until you get a crumbly mixture.
Next, add the egg yolk and sour cream. Using a spatula, start mixing the dough. Then knead the dough by hand until it comes together. Don’t add too much extra flour. I used the amount of flour specified in the recipe. But everyone uses different flour, so some may need a little more or a little less.Leave the dough in the mixing bowl, cover it with plastic wrap and refrigerate for 30 minutes. Meanwhile, let's make the filling. For the vegetable part we’ll need mushrooms, which I cleaned with water and dried with a paper towel. We’ll also need one stick of leek. I cut it in half and cleaned it with water. Chop the leek and slice the mushrooms.
In a frying pan over medium heat, heat 1 tablespoon of butter. Add the leek and cook until softened and slightly browned around the ages. Then remove it from the pan.In the same pan, add another tablespoon of butter. Add the sliced mushrooms and cook until they release their moisture and become golden brown. Towards the end, add a pinch of salt, mix it and when all the liquids have evaporated, remove the mushrooms from the pan. Next, when the dough has chilled, dust the work surface with flour, if needed, place the chilled dough and roll it out thin, about 1/8 of an inch. Lay the dough in the baking pan and push it into the bottom and the sides of the pan. Poke the bottom and the sides of the pan with a fork.Today I used a 9-inch cake pan, but I highly recommend using a springform pan or a removable bottom tart pan with high sides. Using these pans will make it easier to remove the baked quiche from the pan. Next, place a piece of parchment paper on top of the dough and cover it with pie weights, beans, or rice like I did. Bake at 350 F degrees for 15 minutes, then remove the weights and bake for 5 more minutes or until slightly golden. Set it aside and make the custard filling.
In a mixing bowl combine the sour cream, eggs, salt and ground nutmeg. Using a whisk combine all the ingredients.
To assemble the quiche, place the leeks over the pre-baked crust and spread them evenly. Next, spread the mushrooms. Pour the custard mixture over the vegetables. Then spread the cheese on top. Using a fork, mix the cheese into a top layer of custard.If you have some fresh thyme, use it. Fresh thyme pairs well with the delicate flavors of this quiche. Just sprinkle a few leaves on top of the quiche.Bake the mushroom quiche at 350 F degrees for 45-50 minutes. Enjoy it warm or let the quiche cool down to room temperature, cover the top with foil and refrigerate. When the quiche has cooled down, run a knife between the quiche and the baking pan to take the pan off.
