This dressing comes from the Penn State's Housing
and Food Services Department (1987).

1 cup mayonnaise
1 teaspoon onion salt
1/4 teaspoon dried chives (or 1 tsp fresh)
1/4 teaspoon dried parsley (or 1 tsp fresh)
1/4 teaspoon garlic powder
1/4 teaspoon salt
1/4 teaspoon white pepper
pinch of ground dried oregano
1 cup buttermilk

Put mayonnaise, onion salt, chives, parsley, garlic powder,
salt, pepper and oregano into a deep mixing bowl and stir
to combine. Beat mayonnaise mixture with an electric mixer
on low speed for about 5 seconds, then increase speed to
medium and beat until smooth, about 20 seconds.

Scrape dressing down sides of bowl with a rubber spatula.
Increase speed to high and gradually add buttermilk,
beating constantly until all the buttermilk is incorporated
and the dressing is smooth, about 2 minutes more.

Cover and refrigerate dressing for at least 12 hours. Stir
dressing well before serving. Dressing will keep, refrigerated
in a covered container, for up to 2 weeks. Makes 2 cups.

Source: Pittsburgh Post-Gazette, September 2, 2004