Heat the oil in a large skillet over medium heat. Add the leeks and cook until very tender, about 5 to 6 minutes. Cool the leeks to room temperature. Preheat the oven to 350 degrees F. Place the eggs, milk, cream, nutmeg, salt and white pepper in a bowl and whisk to combine. Arrange half the leeks and stilton in the bottom of the pie shell. Pour in egg mixture. Arrange remaining ingredients on top. Bake 40-45 minutes, or until eggs are set. Rest the quiche 5 to 10 minutes before serving to allow filling to set.