01 - Preheat the oven to 350°F. Grease a 9-inch tart pan with butter.
02 - Roll out the shortcrust pastry and line the prepared pan, trimming excess dough. Prick the base with a fork, then chill in the refrigerator for 10 minutes.
03 - Heat olive oil in a skillet over medium heat. Add onion and sauté for 2 minutes until translucent. Add garlic and cook for 30 seconds.
04 - Add spinach to the skillet and cook until wilted and liquid evaporates, about 3 to 4 minutes. Remove from heat and let cool slightly.
05 - In a large bowl, whisk together eggs, milk, cream, nutmeg, salt, and pepper. Stir in half of the grated cheese.
06 - Spread the cooled spinach mixture evenly over the pastry base. Pour the egg mixture on top, then sprinkle the remaining cheese over the surface.
07 - Bake for 35 to 40 minutes, until the filling is set and the top is golden brown.
08 - Allow the quiche to cool for 10 minutes before slicing and serving.