This is a variation of "All-American Barbecue Sauce" found at http://fp.enter.net/--rburk/sauce-rub-marinade/barbecuesauce/all-amer.txt it leaves a little kick in your mouth and you begging for more.
In medium-sized saucepan, heat butter over medium-low heat. Add onion and saute for 5 minutes, but do not allow them to brown.
Stir in ketchup, sugar, Worcestershire sauce, mustard, vinegar. Bring to a boil; reduce heat and simmer, stirring occasionally, for 5 minutes.
Divide into jars, cool and freeze or refrigerate for 2 to 3 weeks.
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