In a food processor, combine the flour and salt. Add the cold, cubed butter and pulse until the butter forms small crumbs. While the processor is running, gradually add the very cold water until a rough dough forms. Transfer the dough onto a large sheet of baking paper, form it into a ball, cover with another sheet of baking paper, and roll it out into a 1/6 inch thick disk. Chill in the fridge for at least 1 hour.

Remove the dough from the fridge and place it in a 10-inch x 1.5-inch quiche pan. Press the dough gently into the sides and bottom of the pan. Chill in the fridge for another hour or preferably overnight.

Preheat your oven to 325°F. While the oven is preheating, place the dough-lined pan in the freezer. Dock the bottom of the pastry with a fork and cover it with baking paper and weights. Par-bake for 15 minutes, remove the weights and paper, and bake for an additional 10-15 minutes. Let it cool.

Rinse and thinly chop half of a leek. In a large frying pan, cook the leek in olive oil over medium heat for about 5 minutes until soft and translucent. Set aside. Cut the smoked salmon into small pieces.

In a large bowl, whisk together the eggs and cream. Add the salt, pepper, garlic powder, dill, and grated Gruyère cheese.

Layer the smoked salmon and cooked leeks over the partially baked quiche crust, alternating between the two.

Pour the egg mixture over the filling. Optionally, top with more grated cheese and any leftover salmon and leek.

Bake in a preheated oven at 350°F for 40-50 minutes, until the custard filling has set. Let it cool for 10-15 minutes before serving. Optionally, top with a dollop of crème fraîche and some fresh dill.