In a large, heavy saucepan, melt butter over medium heat, add onion and saute, stirring now and then until translucent, 6 to 8 minutes.
Add in garlic and stir for a moment longer just until fragrant.
Add the rest of the ingredients and bring to a boil.
Turn down to a simmer, stirring now and then, until reduced to desired consistency, 10 to 15 minutes or so.
Store in a jar in the refrigerator; lasts for two to three weeks.
