Wash and dab off the crusted roast, season with salt and pepper and place on the fat pan of the oven. Peel and quarter 2 white onions. Peel and chop the garlic. Spread onions, garlic and caraway seeds around the roast.
Pour on 2 litres of water and bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for approx. 2 hours. Pour over roast from time to time and add water if necessary. In the meantime, peel the red and remaining white onions.
Cut red onions into large pieces and white onions into slices. Melt the sugar in a pot and deglaze with red wine and vinegar. Add red onions. Season with salt and pepper. Add 2 bay leaves and 2 sprigs each of rosemary and thyme and cook for about 30 minutes until the onions become translucent.
Put white onions, stock and cream in a pot and steam. Add the rest of the bay leaf, rosemary and thyme and cook for about 30 minutes until the onions become transparent. Take the roast out of the oven and keep it warm.
Pour frying stock through a sieve into a pot and bring to the boil. Season to taste with salt and pepper. Stir cornflour with 2 tablespoons of water until smooth and thicken the stock. Cut the crusted roast open and arrange it on a plate with the onion vegetables.
Serve the sauce separately.