Creamy Leek, Potato, and Sour Cream Chive Soup

3 Tb. butter
2-3 leeks, thinly sliced (white and pale green parts only)
1 tsp. dill
1 lb. potatoes, thinly sliced
4 cups chicken or vegetable stock
1 cup sour cream
4 Tb. chopped fresh chives, divided
salt and pepper

Melt butter in pot over medium-low flame. Add leeks and dill; cover and cook slowly, 15-20 minutes. Add potatoes and stock; bring to simmer, cover, and cook until tender, 10-15 minutes. Puree mixture. Return puree to pot; stir in sour cream and 2 tablespoons chives. Add salt and pepper to taste. Sprinkle each serving with additional chives. Makes 6 servings.