Place the steaks in a shallow dish. Mix the marinade ingredients together and pour over the steaks. Leave to marinate, turning the meat occasionally. Melt the butter in a large frying pan. Lift the steaks from the marinade (reserve the marinade for the sauce), add the steaks to the pan and cook for 3-6 minutes on each side, depending on how you like them cooked. Remove from the pan and keep warm. Over a high heat add the wine to the juices left in the pan, gathering up any sediment. Strain the marinade and add to the pan, together with the redcurrant jelly and mustard and stir. Add the plums and heat through.
Pour a little sauce onto each plate and lay the steak on top.