Lettuce Soup

Inspired by a recipe in Epicurious Ingredients: 1 cup chopped onions, scallions, and/or shallots 2 garlic clove, chopped 3 tablespoons unsalted butter 1 teaspoon ground coriander 3/4 teaspoon salt 1/4 teaspoon black pepper 3/4 – 1 cup diced (1/3 inch) peeled...