Remove the fat edges and cut the steaks uniformly thick.
For the marinade, peel and finely chop the onion and garlic. Mix well with the remaining ingredients.
Place steaks in a shallow glass bowl, pour the marinade over them and toss the steaks in it.
Cover the bowl with a lid and refrigerate overnight. Turn the steaks occasionally.
Just before grilling, remove from marinade and grill for about 6-8 minutes on each side, brushing occasionally with remaining marinade, and finish grilling according to desired doneness.
Serve the steaks with e.g. croquettes.