Preheat your oven to 400℉.
Par-bake your pie crust in a pie pan at 400°F for 10 minutes then remove. Reduce the oven temperature to 375°F.
Warm a large skillet over medium heat. Add the olive oil, once warm add the leeks and sauté until soft, about 5-10 minutes. Set them aside to get to room temperature.
In a large bowl, whisk together the eggs, heavy cream, whole milk, salt and pepper.
Place the pre-made pie crust on a rimmed baking sheet, put the sautéed leeks on the bottom.
Pour the egg mixture directly on top of the leeks.
Scatter the grated cheese overtop, allowing it to sink in a bit.
Bake for approximately 30 minutes until golden brown and set. Remove and let the baked quiche cool for at least 15 minutes before digging in.