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