Step 1

Put a rack in the center of the oven and heat oven to 425 degrees. Line a baking sheet with a silicone liner or parchment paper. If you like, you can sprinkle Gruyère or Cheddar onto the center of the liner or paper in an approximate 10-by-13-inch rectangle.

Step 2

In a medium bowl, whisk together egg, Parmesan, lemon zest or rosemary, garlic (if using), and pinch of salt and pepper until smooth. Beat in the crème fraîche until smooth.

Step 3

On a lightly floured surface, roll out the puff pastry to form a 10-by-13-inch rectangle, about 1/8-inch thick. Transfer the dough to prepared baking sheet. (Place directly on top of the grated cheese, if applicable.) With a sharp knife, lightly score a 3/4-inch border around the edges of the puff pastry, making sure not to cut the pastry all the way through. Using a fork, prick the pastry all over inside the border at 1-inch intervals.

Step 4

Spread crème fraîche mixture evenly inside the scored border. Arrange vegetables in an even layer, using just enough to cover the surface in one layer. Scatter scallions and thyme or rosemary sprigs on top. Lightly drizzle with oil, and sprinkle with salt and pepper.

Step 5

Bake until the pastry is puffed and golden, and the vegetables are cooked through, about 25 to 35 minutes. Transfer the pan to a wire rack to cool for at least 15 minutes before serving. Serve topped with microgreens, herbs or baby lettuces, and accompanied by lemon or lime wedges, for squeezing.