Cut the kasseler comb into large elongated pieces. Heat an ovenproof roasting pan with a lid over medium-high heat and fry the meat until well browned on all sides, about 10-12 minutes.
Remove the meat from the pan. Dice the onions into small cubes.
Fry the diced onions in the roasting fat over medium heat until softened, about 5 minutes. Add the sugar and stir constantly until caramelized, about 2-3 minutes. Turn off the heat.
Place the browned meat on top of the caramelized onions. Top with the sauerkraut. Wash the seedless grapes and scatter them over the sauerkraut.
Pour 1 cup of cream over the mixture. Cover the pan with the lid and place in the preheated oven.
Cook for 45-60 minutes at 200°C (392°F). Check halfway through and pour the remaining cup of cream over the casserole if it appears too dry.
The pork is done when it reaches an internal temperature of 63°C (145°F). Serve with mashed potatoes or bread.