Sauce for Asparagus

6 Tbsp chopped onion
2 Tbsp butter
2 cup sour cream
2/3 cup mayonnaise
2 Tbsp lemon juice
1/2 tsp salt
1/4 tsp green pepper
4 pounds cooked fresh asparagus

Sautee onion in butter.  Stir in rest, but do not boil.
Drizzle over the asparagus.