01 - Preheat the oven to 375°F.
02 - In a bowl, combine flour and salt. Cut in the cold butter using a pastry cutter or fingertips until the mixture resembles coarse crumbs. Add ice water, 1 tablespoon at a time, mixing until dough just comes together. Shape into a disc, wrap in plastic, and refrigerate for 20 minutes.
03 - Roll out the dough on a lightly floured surface to fit a 9-inch tart or pie pan. Press into the pan, trim excess, and prick the base with a fork. Line with parchment and fill with pie weights. Bake for 15 minutes, remove weights and parchment, and bake for 5 more minutes. Remove from oven and set aside.
04 - Heat olive oil in a skillet over medium heat. Add asparagus, leeks, and peas. Sauté for 3–4 minutes until just tender. Stir in spinach and cook until wilted, about 1 minute. Remove from heat and let cool slightly.
05 - In a large bowl, whisk together eggs, milk, cream, salt, pepper, and nutmeg. Stir in cheese and chives.
06 - Spread the sautéed vegetables evenly over the pre-baked crust. Pour the egg mixture over the vegetables.
07 - Bake for 25–30 minutes, or until the custard is set and the top is lightly golden.
08 - Let cool for at least 10 minutes before slicing and serving.