Clean and cut in cubes all the vegetables. In the same saucepan or iron cast, reheat butter and sauté onion for 2-3 minutes. Add all the vegetables, bay leaves, allspice (place it in tea steeper) and season with salt and pepper. Sauté for another 5 minutes. Add 4 cups of water.
If you use an iron cast, make a nest from the vegetables and place directly the seared meat in the vegetables. If you are using an oven safe dish, transfer the sauté vegetables in the oven safe dish, then add the water and the meat. Cover with the lid and braise in preheated oven 160 C / 320 F for 2 hours. Baste the meat every 30 minutes, so it stays juicy.
After two hours of braising, remove the iron cast / oven safe dish on working surface and transfer the meat to a plastic or ceramic container with the lid. Close the lid and let the meat stand. Leave all the baked vegetables in the iron cast and remove the bay leaves and allspice. Discard these spices. If you use oven safe dish, transfer all the vegetables and juices in the large saucepan.
Place the iron cast/saucepan on the stove and heat the vegetables on medium heat. Add sugar, mustard Dijon and honey mustard. Let it bring to light simmer. Then remove it from the stove top and blend the vegetables with a hand blender to the smooth consistency.
Add lemon juice from 1 lemon, vinegar, sour cream and heavy cream 35%. The sauce should be creamy, and the consistency should be as a thick soup or pottage. If the sauce is too thick, add more water or instant thickener to thicken the sauce.