Heat the butter in a pan. Sauté the shallots and garlic for approx. 5 mins. Add the juniper, bay leaf and rosemary, briefly sauté. Pour in the Marsala and stock, reduce for approx. 2 mins. Add the plums and sugar, simmer for approx. 5 mins. Reduce the heat and remove the pan from the hob. Gradually whisk in the butter. Return the pan to the hob a few times to gently warm the sauce; it must not boil. Stir until the sauce thickens.
Heat the clarified butter in a frying pan. Season the meat, brown for approx. 2 mins. on each side. Remove, cover and leave to rest for approx. 5 mins. Serve the meat with the plum sauce.