Preheat your oven to 180°C (350°F). Roll out the store-bought pie crust on a floured surface to fit your pie dish, then gently transfer it into the dish, trimming any excess edges. Prick the bottom with a fork and blind bake for 10 minutes until lightly golden.
Meanwhile, clean the leeks thoroughly to remove dirt between layers, then slice them thinly. In a skillet, melt the butter or heat the olive oil over medium-low heat. Add the sliced leeks and a pinch of salt, cooking slowly for about 15 minutes until they are soft, fragrant, and caramelized to a golden hue.
In a mixing bowl, whisk together the eggs, heavy cream, salt, pepper, and nutmeg until smooth and slightly frothy. Stir in the grated cheese, reserving a little for topping.
Spread the caramelized leeks evenly over the baked crust, then pour the custard mixture over them, ensuring the leeks are well covered. Sprinkle the remaining cheese on top for a golden, cheesy crust.
Bake the quiche in the oven for 30 to 35 minutes, until the top is golden brown and the filling is just set with a slight jiggle in the center. The aroma should be rich and inviting.
Remove the quiche from the oven and let it rest for about 10 minutes. This helps the filling to set and makes slicing easier. The crust should be crisp, and the filling creamy and tender.
Slice the quiche and serve warm or at room temperature, enjoying the layered sweetness of the leeks combined with the sharp cheese in a flaky crust.
