How to Make It
In a bowl, whisk the sherry vinegar with the lemon juice, rosemary and garlic. Pour the marinade into two large, resealable plastic bags. Add the ribs, seal the bags and turn to coat the ribs. Let the ribs marinate at room temperature for 1 hour, turning the bags halfway through.
In a food processor, combine all of the ingredients except the olive oil, vinegar, salt and pepper. Pulse until the herbs are finely chopped. Add the olive oil and vinegar and pulse to combine. Season the chimichurri with salt and pepper and transfer to a bowl.
Light a grill. Remove the ribs from the marinade. Scrape off the garlic and rosemary and pat the ribs dry with paper towels. Brush the ribs with oil and season with salt and pepper. Grill the ribs over moderately high heat, turning, until nicely charred outside and medium-rare, 10 to 12 minutes. Transfer to a platter and serve with the chimichurri.