Mix the flour and salt in a bowl, then cut in the cold butter until the mixture resembles coarse crumbs. Gradually add ice water, a tablespoon at a time, until the dough begins to come together. Press the dough into a disk, wrap in plastic, and chill for at least 30 minutes.
Preheat your oven to 180°C (350°F). Roll out the chilled dough on a lightly floured surface to fit your tart pan. Transfer it carefully, pressing into the edges, and trim the excess. Chill the crust for 10 minutes to relax the gluten.
Line the crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes until the edges are starting to turn golden. Remove the weights and parchment, then bake for another 10 minutes until fully golden and crisp.
While the crust bakes, melt the butter in a skillet over medium-low heat. Add the sliced leeks and cook slowly, stirring occasionally, until they are soft and slightly caramelized, about 10 minutes. Let them cool slightly.
In a bowl, whisk the eggs, heavy cream, black pepper, and a pinch of nutmeg if using. Stir in the grated cheese until combined.
Spread the cooled leeks evenly over the baked crust. Pour the egg and cheese mixture over the leeks, making sure it’s evenly distributed.
Bake the quiche at 180°C (350°F) for 35-40 minutes, until the filling is puffed, slightly golden, and just set in the center. Check at 35 minutes; if the top is browning too fast, tent with foil.
Remove the quiche from the oven and let it rest for about 10 minutes. The filling will firm up, making slices neater and easier to serve.
Slice the quiche into wedges and serve warm or at room temperature, enjoying the tender leeks and gooey cheese in every bite.
