Peas with Spinach and Bacon in Lettuce Cups

Name: Peas with Spinach and Bacon in Lettuce Cups
Ingredients: 4 slices bacon, cut into 1/2-inch pieces; 2 tablespoons unsalted butter; 2 leeks (white and pale-green parts only), halved, thinly sliced into half moons, and rinsed well (2 cups); Coarse salt and freshly ground pepper; 20 ounces spinach, tough stems removed, washed well (8 packed cups); 2 cups shelled fresh garden peas (from 2 pounds in pods); 1/2 cup chicken broth; 1 tablespoon finely chopped mixed fresh herbs, such as dill, chervil, and tarragon; 12 leaves Boston or Bibb lettuce