In a small sauté pan, melt butter over medium heat. Add leeks. Cook until soft, 6 to 8 minutes. Add peas, tarragon, and parsley. Cook until heated through, 3 to 4 minutes. Add goat cheese, salt, and pepper, stirring until smooth.
Transfer mixture to a large bowl, and let cool for 15 minutes. Add eggs to cooled leek mixture, gently whisking until well combined.
Preheat oven to 350°. Spray with cooking spray 12 (4½x2½-inch) rectangular tart pans with removable bottoms.
On a lightly floured surface, roll each piecrust into a 12-inch round. Cut each crust into (6½x4½-inch) rectangles, rerolling scraps as necessary but no more than twice.
Place dough rectangles in tartlet pans, pressing firmly into bottoms and up sides, crimping edges, if desired. Lightly prick bottoms several times with a fork.
Bake until edges are just golden, about 10 minutes.
Divide leek filling evenly among tartlet shells.
Bake until centers are set, 12 to 15 minutes. Let cool in pans for 5 minutes. Garnish with a sprig of tarragon, if desired.
Recipe by Victoria at https://victoriamag.com/sweet-pea-and-leek-tartlets-recipe/