1/2 c. sour cream
1/2 c. real mayonnaise
1/2 c. Parmesan cheese, grated
1/2 c. onion, grated or finely chopped
1/2 c. fresh parsley (cut fine or chopped)
1/2 tsp. Worcestershire sauce

Mix together, refrigerate for at least 2 hours or overnight. Plain yogurt with a couple tablespoons of whipping cream mixed in can be substituted for sour cream. If an onion as mild as a Vidalia is used, the full 1/2 cup of onion can be added with the other ingredients; if a stronger onion is used, go by taste.