Preheat your oven to 160°C/320°F.
In an ovenproof casserole dish, mix the butter, sugar, vinegar, salt and 7 cl of water.
Heat, covered, over medium heat until the butter is melted and the ingredients are well combined.
Add the red cabbage, grapes and herbs and mix well to coat.
Bring to the boil, cover the casserole dish and place in the oven.
Let cook for 2 hours, stirring every 1/2 hour and adding a little water if necessary.