01 - In a bowl, combine flour and salt. Add cold butter and cut in using a pastry blender or fingers until mixture resembles coarse crumbs. Add ice water, 1 tablespoon at a time, mixing just until dough holds together. Shape into a disk, wrap in plastic, and chill for 30 minutes.
02 - Preheat oven to 375°F. On a lightly floured surface, roll out dough to fit a 9-inch tart pan. Press into pan and trim edges. Prick base with a fork. Line with parchment and fill with pie weights. Bake for 15 minutes, remove weights and parchment, and bake 5 minutes more. Let cool slightly.
03 - Heat olive oil in a skillet over medium heat. Add asparagus and scallions; sauté for 2–3 minutes. Add spinach and peas; cook until wilted and bright green, 1–2 minutes. Remove from heat.
04 - In a bowl, whisk together eggs, milk, cream, salt, pepper, and nutmeg until fully combined.
05 - Spread sautéed vegetables over crust. Top evenly with Gruyère and feta. Pour egg mixture gently over filling.
06 - Bake quiche 30–35 minutes until the center is just set and top is golden. Cool 10 minutes before slicing.