Cream of Asparagus Soup (Crème d'asperges)

Cut tips from 12 asparagus 1 1/2 inches from top and halve tips lengthwise if thick. Reserve for garnish.

Cut stalks and all remaining asparagus into 1/2-inch pieces.

Cook onion in 2 tablespoons butter in a 4-quart heavy pot over moderately low heat, stirring, until softened. Add asparagus pieces and salt and pepper to taste, then cook, stirring, 5 minutes. Add 5 cups broth and simmer, covered, until asparagus is very tender, 15 to 20 minutes.