preheat oven to 375°F. Bake pie shell on middle rack of oven 10 min

meanwhile, in a skillet, heat oil over medium-heat. Add leeks and mushrooms and cook until leeks are tender, mushrooms are golden and no liquid remains, about 8 minutes. season with salt and pepper.

Turn oven to 425°F.

In a bowl, whisk together eggs, milk and thyme. sprinkle 1/2 cup cheese over bottom of pie shell. Spread mushroom mixture evenly over cheese. Pour egg mixture overtop and sprinkle with remaining cheese.