Preheat your oven to 190°C (375°F). Roll out your pie crust on a lightly floured surface until about 3mm thick, then fit it into your pie dish, trimming the edges. Poke the crust with a fork all over and blind bake on a baking sheet for 15 minutes until lightly golden.
While the crust bakes, thinly slice the leeks and melt the butter in a skillet over medium-low heat. Add the leeks, season with a pinch of salt, and cook slowly, stirring occasionally, for about 20 minutes. The leeks should turn deep golden, smell sweet, and develop a smoky aroma.
Remove the caramelized leeks from the skillet and spread them evenly over the pre-baked crust. In a bowl, whisk together eggs, heavy cream, salt, pepper, and nutmeg until smooth and just combined.
Sprinkle the shredded cheddar cheese over the leeks, then pour the custard mixture evenly on top. The filling should come close to the edge of the crust but not overflow.
Bake the quiche for 35-40 minutes, until the edges are golden and the filling is just set with a slight wobble in the center. If the top browns too quickly, tent with foil to prevent burning.
Remove the quiche from the oven and let it rest on a cooling rack for at least 10 minutes. This helps the filling to set fully and makes slicing easier.
Slice the quiche into wedges with a sharp knife, ensuring each piece has a crisp crust and a creamy, cheesy filling. Serve warm or at room temperature, enjoying the tender leeks and rich cheese in every bite.
