Peel off the garlic cloves, chop finely and mix with the liquid ingredients and black pepper to form a marinade. Carefully cut into the meat at a distance of approx. 2 cm so that the marinade can penetrate better.
Put the flank steak together with the marinade in a sealable freezer bag so that the meat is completely covered in the marinade. Put the bag in the refrigerator for at least 2 hours, or preferably overnight.
To grill, take the flank steak out of the bag and drain off the excess marinade. Salt and pepper well and grill over high heat for 4 - 6 minutes on each side.
Then take it off the grill, wrap it in aluminum foil and let it rest for 8-10 minutes so that the meat juice can spread out. Then thinly slice the flank steak against the grain and serve.