Lightly chop the rosemary leaves and add them to a bowl with the oregano.
Thinly slice the garlic cloves and add them to the bowl.
Add the mustard and the balsamic vinegar to the bowl. Slightly mix all the ingredients.
Add the olive oil slowly and whisk until fully incorporated.
Marinate the meat for a minimum of two hours and up to 24 hours.
Grill, broil, or pan-sear the meat until you have reached your desired doneness.
Notes
Once cooked, store the leftovers in an airtight container in the refrigerator for up to three days. The steak can be marinated and then frozen. Thaw in the refrigerator before cooking. The marinade can be made ahead and stored in the refrigerator for up to a week.