In a saucepan combine vinegar, water, cane sugar, salt and mustard seeds. Bring to a boil. Remove from the heat and set aside.
In a large saucepan melt the butter with olive oil. Add onions and cook, until tender. Add apples and vinegar mixture. Bring to a boil over high heat, reduce the heat and simmer, uncovered, until apples are just tender. Add dried mint and thyme, and cook for about 5 minutes.