Ingredients
4 tablespoons unsalted butter
3 large leeks, white and light-green parts only, sliced and well washed (6 cups)
Kosher salt and freshly ground pepper
2 Yukon Gold potatoes (about 1 pound total), peeled and cut into 1-inch pieces (2 cups)
1 cup homemade or store-bought vegetable broth
1 1/2 cups shelled fresh or frozen peas
2 packed cups baby spinach or stemmed spinach leaves
Whisked crème fraîche and fresh chervil leaves, for serving (optional)
Preparation
Prepare an ice-water bath. Melt butter in a medium saucepan over medium-high heat. When foam subsides, add leeks, season with salt, and cook, stirring, until translucent, 5 minutes. Add potatoes, broth, and 3 cups water. Bring to a boil, then reduce heat to medium-low and simmer, partially covered, 10 minutes.
Add peas; simmer until tender, about 5 minutes (or 2 minutes, if frozen). Stir in spinach and remove from heat; let stand 5 minutes.
Working in batches, transfer soup to a blender and purée until very smooth, 1 to 2 minutes a batch (remove center cap from lid and cover opening with a clean kitchen towel, which allows steam to escape). Strain through a fine-mesh sieve, if desired, for silkiest texture.
Transfer to a large bowl (ideally metal); set bowl in ice bath. Let cool completely, stirring occasionally, about 30 minutes. Transfer to an airtight container and refrigerate until cold, at least 4 hours and up to 3 days. Season with salt and pepper; thin with more water or broth if too thick. Serve in small cups, each with a dollop of crème fraîche, a sprig of chervil, and a sprinkle of pepper.
