01 - Combine flour and salt in a large bowl. Cut in cold butter using a pastry blender or fingertips until mixture resembles coarse crumbs. Gradually add 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 out the chilled dough into a 12-inch circle. Transfer to the prepared baking sheet.
05 - Spread half the crumbled goat cheese over the center of the dough, leaving a 2-inch border. Arrange sautéed vegetables over the cheese. Sprinkle with thyme, lemon zest, salt, pepper, and the remaining goat cheese.
06 - Fold the edges of the dough up over the filling, pleating as you go, to form a rustic edge, leaving the center exposed.
07 - Whisk together egg and milk. Brush over the pastry edge.
08 - Bake for 35–40 minutes, or until the crust is golden brown and crisp. Let cool for 10 minutes before slicing.