Seal well the beef in a sauté pan, remove and using the same pan sauté the quartered prunes, shallots and livers until browned. Add the sugar thyme and caramelize than pour in the port, wine and simmer. Finish the oven in the oven until cooked to your likings. Peel, slice and boil the potatoes, meanwhile dilute the gorgonzola in the cream and mix together with the boiled potatoes. Spread the potatoes in a small oven tray top with the cheddar slices and sprinkle with grated cheese than bake until lightly browned at the top, allow to rest than cut with a cutter. Serve with the cooked beef fillet mignons.