Filling
¼ cup combined olive oil and butter
300 grams thinly sliced onions
150 grams aged Gruyère cheese, grated
3 eggs, beaten
½ cup heavy cream
sea salt, freshly ground black pepper, freshly ground nutmeg
6–8 black French olives, pitted
Olive oil pastry
1 cup flour
½ tsp salt
¼ cup olive oil cold water
Combine flour, salt, and olive oil in mixing bowl, stirring until olive oil is dispersed in small lumps throughout the dough. Little by little, add water and stir into flour mixture until slightly sticky dough is formed. Roll out dough on generously floured surface, and line fluted quiche pan.
Heat butter and oil mixture in saucepan and gently sauté onions on medium heat until transparent (about 15–20 minutes), without browning. In large bowl, combine Gruyère, beaten eggs, cream, salt, pepper, and nutmeg, then add (cooled) onions. Stir together thoroughly and pour into tart shell.
Bake for 30 minutes in preheated 400℉ oven. When cooked, decorate top with olives and serve.