Cream of Asparagus soup

This recipe was easy and good. I will add at least 2 potatoes next time to make it thicker.

2 lbs asparagus (2 bunches)
1 tbsp butter
1 onion, chopped
2 potatoes, peeled and diced
6 cups chicken broth
2 tbsp low fat sour cream
salt and fresh pepper to taste
In a large pot, melt better on low heat. Add onion and sauté on low for about 2-3 minutes. Add potato to the pot with the onions. Snap the tough ends off the asparagus and discard. Chop the asparagus into 2 inch pieces. Saute onion, potato, and asparagus in butter. Add chicken broth, salt and pepper. Cover and cook about 20-25 minutes or until asparagus is very tender. Remove from heat, add sour cream and transfer in batches to blender, puree until smooth.