Wash the meat and dab dry. Peel onion and carrots. Wash the carrots and cut them into large pieces. Heat lard in a large roasting pan with lid. Brown the meat thoroughly all around.
Season with salt and cayenne pepper. Add onion and fry for about 3 minutes. Pour on the cola and rum. Add spices. Bring everything to the boil.
Cover in a preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) and braise for 3 1⁄2-4 hours. Turn meat once in between.
Lift the roast out of the stock and let it drain briefly. Pour the braising stock through a sieve into a small pot and degrease. Bring to the boil, simmer for about 5 minutes. Stir starch with 5 tbsp. cold water until smooth. Bind the stock with it and simmer for about 2 minutes.
Season the sauce with salt. Dress everything. Serve with American potato salad.