Creamy Green Pea Soup

Name: Creamy Green Pea Soup
Ingredients: 4 tablespoons unsalted butter; 8 medium shallots (about 5 ounces), minced (about 1 cup), or 1 medium leek, white and light green parts chopped fine (about 1 1/3 cups); 2 tablespoons unbleached all-purpose flour; 3 1/2 cups low-sodium chicken broth; 1 1/2 pounds frozen peas (about 4 1/2 cups), partially thawed at room temperature for 10 minutes (see note); 12 leaves Boston lettuce (about 3 ounces) from 1 small head, leaves washed and dried; 1/2 cup heavy cream