1-Prepare the savory shortcrust pastry: In a bowl, mix 180 grams of plain flour and 1 pinch of salt. Cut in 90 grams of very cold unsalted butter until the mixture resembles coarse crumbs, then add 60 milliliters of cold water and knead gently until dough forms. Roll it out and press into a tart pan.

2-Sauté the leeks and onion: In a skillet, heat 30 grams of unsalted butter or olive oil over medium heat. Add the thinly chopped 2 leeks, 1 small thinly sliced brown onion, and 1/2 teaspoon of minced garlic, cooking until soft and caramelized, about 8-10 minutes.

3-Prepare the filling: In a separate bowl, whisk together 2 large eggs, 120 milliliters of heavy or thickened cream, 1 teaspoon of table salt, 1/2 teaspoon of pepper, and 1 teaspoon of ground cumin if using.

4-Assemble the tart: Blind bake the pastry in the preheated oven for 10 minutes to keep it crisp. Then, spread the sautéed leek mixture evenly over the crust and pour the egg mixture on top. Sprinkle 35 grams of grated Gruyere cheese over everything.

5-Bake the tart: Place in the oven and bake for 30-35 minutes until the filling is set and golden. Let it cool for a few minutes before slicing to maintain that moist texture.