Chutneys are wonderful accompaniments to braises or charcuterie boards.
Heat the butter and sugar in a medium saucepan until the sugar melts and is bubbling well. If you have a laser thermometer, it should read 235° F.
Add the vinegar. Stir the ingredients with a wooden spoon, making sure to reach the edges of the pan. Bring the ingredients back to a boil and allow it to reduce to a thick syrup. Add the remaining ingredients, stir with the wooden spoon and lower the heat. Cook until the onions are soft.
Adjust the seasoning and store to cool.