Salt the lamb joint and grind some black pepper onto its surface. Melt the butter in a pan, and brown the joint by frying and turning it in the pan. Lift the joint into a baking dish lined with SAGA Cooking Paper.
Measure out the cola drink, cherry juice, soy sauce and finely chopped garlic into a bowl. Add some freshly-ground black pepper and rosemary. Bring the mixture to the boil to reduce it a bit. Baste the joint with the liquid. First, roast at 225 °C for 15 minutes. Reduce the temperature to 125 °C and roast until the inner temperature of the joint is 56–58 °C. Baste the joint several times during roasting.
Take the meat out of the oven and let it rest for about 15 minutes. Only then remove the meat thermometer and slice the meat.
Serve with roasted root vegetables.