An hour before making the sauce, open the can of beer and pour it into a measuring cup or bowl. Let it stand until bubbles has dissipated.
In a medium saucepan, melt butter and saute onion over medium heat until translucent. Add garlic and cook for 30 seconds. Add remaining ingredients and simmer sauce on medium low heat for 10 minutes, stirring occasionally. Watch for burning and reduce heat to low if needed.
Remove sauce from heat and cool for 10 minutes. Place into a blender or food processor and puree mixture. Use it to baste meats during the last half an hour of cook time. You can also serve this barbecue sauce on the side.
Store sauce in an air tight container in the refrigerator for up to 1 week after preparation. Reheat before using.