In a large bowl, whisk together the flour and salt until well combined.

Add the cold, cubed butter to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs.

Gradually add ice water, one tablespoon at a time, mixing gently after each addition. Keep adding water until the dough just comes together; it should be moist but not sticky.

Turn the dough out onto a lightly floured surface. Gently form it into a disk and wrap the disk tightly in plastic wrap. Refrigerate it for at least 30 minutes or up to 2 hours to let it chill.

On a lightly floured surface, roll out the dough into a 12-inch circle, aiming for a consistent thickness.

Carefully transfer the rolled-out dough to a 9-inch pie plate. Gently press the dough into the bottom and up the sides of the plate, then trim any excess that hangs over the edge for a neat finish.

Crimp the edges of the crust using your fingers or a fork for a decorative touch.

Preheat your oven to 375°F (190°C). Line the crust with parchment paper and fill it with pie weights or dried beans. Bake for 15 minutes.

Remove the parchment paper and pie weights, then bake for another 5-10 minutes, or until the crust is lightly golden brown. Let the crust cool slightly while you prepare the filling.

Heat the olive oil in a large skillet over medium heat. Add the chopped onion and leeks, cooking until softened, about 5-7 minutes.

Stir in the minced garlic and cook for another minute until fragrant, filling your kitchen with a mouthwatering aroma.

Remove the skillet from the heat and stir in the flaked salmon, dill, and parsley until well combined. Set the mixture aside.

In a large bowl, whisk together the eggs, heavy cream, milk, salt, pepper, and a pinch of nutmeg until smooth and well-combined.

Stir in the grated Gruyere cheese, letting it melt beautifully into the mixture.

Pour the salmon and vegetable mixture into the pre-baked crust, spreading it evenly over the bottom.

Gently pour the egg mixture over the salmon and vegetable mixture, ensuring that the filling is evenly distributed throughout.

Bake in the preheated oven for 35-45 minutes, or until the filling is set and lightly golden brown. The center of the quiche should be just slightly jiggly, promising a creamy texture.

Remove the quiche from the oven and let it cool for at least 15 minutes before slicing and serving. This cooling time allows the flavors to meld beautifully.