Place the Flour and Salt in the bowl of a food processor. Add the cold Butter cut into small cubes and blend until it forms small crumbs.

Slowly add the cold Water, a little at a time, blending between each addition. Stop adding the water as soon as the dough comes together.

Transfer the dough to a lightly floured sheet of baking paper and bring together into a disk. Place a second sheet of baking paper over it and roll the pastry into a large rectangle. Place in the fridge to rest for at least 1 hour.

Remove the layers of baking paper and line a baking pan with the Shortcrust Pastry. Poke small holes all over the pastry with a fork. Refrigerate for 30 minutes to 1 hour, then place in the freezer for the last 15 minutes before baking.

Blind Bake the Pastry for 10 to 15 minutes in an oven preheated to 180°C/350°F, then set aside while preparing the filling.

Wash the Leeks and chop into thin slices. Thinly slice the Brown Onion.

Heat the Butter in a non-stick pan over medium heat. Sauté the Leeks, Onion, and Minced Garlic for about 5 minutes, until the onions are translucent. Remove from heat.

In a separate bowl, whisk together the Eggs, Heavy Cream, Salt, Pepper, and Cumin. Add the pre-cooked Leeks and Onion, then mix in the grated Gruyere.

Pour the filling over the pre-baked pastry and bake for another 25 to 35 minutes, until the leeks are lightly golden and the filling is set. Serve warm.