01 - Combine flour and salt in a large bowl. Add cold butter cubes and cut in with pastry blender or fingertips until mixture resembles coarse crumbs. Gradually drizzle in ice water, mixing just until dough comes together. Shape into a disk, wrap in plastic, and refrigerate for 30 minutes.
02 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
03 - Heat olive oil in a skillet over medium heat. Add asparagus, carrots, sugar snap peas, and a pinch of salt. Sauté for 3–4 minutes until just tender. Stir in radishes and scallions; cook 1 minute more. Remove from heat and let cool.
04 - On a lightly floured surface, roll chilled dough into a 12-inch circle. Transfer to prepared baking sheet.
05 - Spread half the crumbled goat cheese over the dough center, leaving a 2-inch border. Arrange sautéed vegetables over cheese. Sprinkle with thyme, lemon zest, salt, pepper, and remaining goat cheese.
06 - Fold dough edges up over filling, pleating as you go, to create a rustic border while leaving center exposed.
07 - Whisk egg and milk together. Brush mixture over pastry edge.
08 - Bake for 35–40 minutes until crust is golden brown and crisp. Cool for 10 minutes before slicing.