Melt the butter in a large skillet over medium heat.
1 tablespoon unsalted butter
Reserve a few leek rounds and mushrooms to arrange decoratively on the top of the quiche. Add the remaining leeks and mushrooms and cook, stirring occasionally, until tender, about 10 minutes. Transfer to a plate and let cool slightly.
2 small leeks, 1 cup sliced mushrooms
Meanwhile, add eggs, milk, cream, salt, and pepper into a blender and blend for 30 seconds to 1 minute. Set aside.
1 teaspoon salt, 4 large eggs, 1 cup milk, 1 cup heavy cream, ½ teaspoon pepper
Place an aluminum foil sheet inside of a baking sheet. Make sure that the foil is long enough to cover the sides of the tart pan. Use a second sheet if necessary. Place the tart pan on top of the foil.
Evenly spread the leek and mushroom mixture in the bottom of the baked crust.
Sprinkle the herbes de Provence over the top.
½ teaspoon herbes de Provence
Sprinkle the Parmesan cheese over the top.
1 cup Parmesan cheese
Pour egg mixture over the top and bake for 45-50 minutes. About 15 minutes into the baking cycle, arrange your leek rounds and mushrooms decoratively on top. Finish baking. The quiche is done when the filling is set and lightly browned. Remove to a wire rack and allow to cool.