Vegetable Galette

Whisk the flour, salt, and pepper together in a large bowl. Place a box grater over the bowl and grate the butter on the large holes. Gently toss the grated butter in the flour to distribute it evenly. Stir in the ice water with a fork until the flour mixture is evenly moistened. If the dough seems very dry, add 1 to 2 teaspoons more water and stir to thoroughly combine. Scrape the dough onto a work surface, gather up any crumbs, and knead gently just until the dough comes together, about 2 minutes. Shape it into a disk, wrap it in plastic wrap, and refrigerate until well chilled, about 1 hour.
On a lightly floured piece of parchment paper, roll out the dough to a 14-inch (35-cm) round. Slide the parchment paper, with the dough, onto a rimmed baking sheet and refrigerate for 15 minutes.

Preheat the oven to 450°F (232°C).
While the dough is in the fridge, slice the carrots on the diagonal to 1/8-inch to 1/16-inch (3-mm to 1 1/2-mm) thickness. Slice the potatoes to 1/8-inch to 1/16-inch (3-mm to 1 1/2-mm) thickness. Trim the asparagus spears and cut them into 1 1/2-inch (4-cm) lengths. Cut the scallions into 1 1/2-inch (4-cm) lengths.
In a large bowl, gently toss the carrots, potatoes, asparagus, scallions, oil, and lemon zest until completely coated. Season with salt and pepper.
In a small bowl, stir the sour cream or quark and Parmesan together. Take the dough out of the fridge and spread the cream mixture evenly over the dough, leaving a 1 1/2-inch (4-cm) uncovered edge all around. Scatter the vegetable mixture on the cream mixture. Fold the edge of the pastry up and over the vegetables to create a folded-over border and an exposed center. Lightly brush the edge of the dough with milk, being careful not to let any milk drip beneath the dough.
Bake the galette for 20 to 25 minutes, until the pastry is lightly browned and the vegetables are tender. Let the tart cool slightly on the baking sheet. Slide the parchment paper and tart onto a cutting board and cut it into wedges. Serve hot, warm, or at room temperature.