Mix together the oil and Worcestershire sauce in a bowl, then smear this over the steaks, either with a pastry brush or by dipping steaks straight into the bowl.
Heat a heavy based frying pan, and cook the steaks for about 3 minutes each side depending on the thickness and how you like it done.
Wrap them in foil to rest on a warm plate, while you make the sauce.
With pan still on the heat but turned down low, add the butter and let it melt then finely chop the needles from the rosemary sprig and add them to the pan.
Finely chop the garlic clove into the pan, then pour in the port, letting it sizzle and reduce slightly.
Unwrap the steaks and add any juices from the foil parcel to the sauce. Then put steaks on a plate and pour sauce over them.
