heat butter in med sauce pan until foamy
add onion and cook till softened (2 - 3 min)
add garlic and chili powder
cook stirring constantly until fragrant (about 20 sec.)
add tomato juice, 1/2 cup vinegar,worcestershire sauce, mustard, chipotle, molasses, and salt
bring heat to high and bring to simmer
lower temp to medium and continue to simmer stirring occationaly
when sauce is slighly thickened and reduced to 1 1/2 cup (30 - 40 min)turn off heat and stir in pepper and remaining vinegar (1/4 cup)
cool to room temperature