Step 1

Let 3/4 cup frozen peas sit at room temperature to thaw. Meanwhile, prepare the crust.

Step 2

Freeze 1 stick cold unsalted butter until firm, about 15 minutes. Meanwhile, place 1 1/2 cups all-purpose flour and 3/4 teaspoon of the kosher salt in a large bowl and whisk to combine.

Step 3

Place a box grater over a large piece of parchment paper or cutting board. Grate the butter on the large holes of a box grater. When you get down to a small nub of butter, chop that nub into 5 to 6 small pieces.

Step 4

Transfer the butter to the dry ingredients and reserve the parchment paper for baking. Use your fingers to toss the butter in the flour, breaking up any clumps, until evenly coated.

Step 5

Drizzle 1/4 cup plus 3 tablespoons ice water over the butter-flour mixture. Use your hands to combine and lightly mix until a rough dough ball forms; do not overwork the dough.

Step 6

Transfer the dough onto a sheet of plastic wrap and shape into a disc. Wrap completely in the plastic wrap. Refrigerate for at least 1 hour or up to 3 days. Meanwhile, let 1 (5.2-ounce) package Boursin Garlic & Fine Herbs cheese sit at room temperature for at least 30 minutes or up to 1 hour. Prepare the filling.

Step 7

Trim and halve 1 medium leek lengthwise, then rinse between the layers to clean. Thinly slice the white and light green parts crosswise (about 1 cup). Trim 1 bunch asparagus and cut into 1-inch pieces (about 3 cups). Trim and thinly slice 3 ounces radishes (about 2/3 cup). Finely grate the zest of 1 medium lemon; reserve the zested lemon for another use.

Step 8

Heat 2 tablespoons of the olive oil in a large skillet over medium heat until shimmering. Add the leeks and cook, stirring occasionally, until softened but not browned, about 4 minutes. Add the asparagus, remaining 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Cook, stirring occasionally, until bright in color, about 2 minutes. Remove from the heat. Add the peas, radishes, and lemon zest, and stir to combine.

Step 9

Arrange a rack in the middle of the oven and heat the oven to 400°F. Lightly dust the reserved parchment with all-purpose flour.

Step 10

Unwrap the dough and place on the parchment. Lightly flour a rolling pin and roll the dough into a 12-inch round about 1/8-inch thick.

Step 11

Spread the Boursin evenly onto the dough, leaving a 2-inch border. Slide the parchment and dough onto a baking sheet.

Step 12

Spoon the vegetable mixture onto the cheese and arrange into an even layer. Gently fold the edges of the dough over the filling, pleating it about every 2 inches. Brush the crust with the remaining 1/2 tablespoon olive oil.

Step 13

Bake until the crust is firm and golden-brown and the vegetables are tender, 35 to 40 minutes. Let the galette cool for 10 minutes before serving. Serve warm or at room temperature, cut into wedges.