Toast the garlic and onion (optional): Add the garlic and onion to a small dry skillet over medium heat. Toast, stirring constantly, until barely golden, 2 to 3 minutes. Transfer to a small bowl and set aside to cool slightly, about 3 minutes.
Combine the ingredients & whisk everything together until evenly combined.
Transfer to an airtight jar or container. Store in a cool, dry place for up to 6 months.