To make the butter: In a small bowl, using a fork, mix the herbs, cumin, a pinch of salt and a some grinds of pepper into the butter.
Squeeze the juice from the lime into the butter and mix it. Using a spatula, scrape the butter out of the bowl onto waxed paper or plastic wrap.
Roll the paper over the butter and form a log. Continue rolling the paper, or plastic, around the butter and twist both ends. Refrigerate until ready to use. Keep up to 4 days, or freeze up to 1 month.
In a food processor, combine the olive oil, vinegar and garlic and process until finely chopped. Season the steaks with salt and pepper and place them in a dish, then add the marinade and turn to coat. Place in the fridge for about 30 minutes to 2 hours. Heat the grill and oil the grill rack, or preheat a broiler.
Remove the steaks from the marinade. Place the steaks on the grill rack, or put them on a baking sheet and place under the broiler. Cook, turning the steaks once, for about 8 minutes total for medium-rare, or until done to your liking. Top the steaks with the butter and serve immediately.