Procedure:
Melt butter in a heavy saucepan.
Saute onions in the butter for 3 minutes.
Add remaining ingredients.
Bring to a boil, stirring frequently.
Reduce heat and simmer until sauce is reduced to about 2 2/3C (630ml), which takes approximately 30 minutes.
Season with salt and pepper.
Note: Sauce can be prepared ahead and held refrigerated for 1 week.
