Heat a cast iron skillet over medium-high heat. Rub the steaks on both sides with the cut side of a garlic clove. Finely chop one sprig of rosemary. Season the steaks with salt, pepper and rosemary, drizzle with EVOO and cook for 9-10 minutes, turning once for medium-rare doneness. Rest the meat, then thinly slice it against the grain.
Meanwhile, place the shallot, arugula, basil, parsley, thyme or oregano, sage, the leaves of the remaining sprig of rosemary, the remaining clove of garlic, grated or pasted, salt, pepper, vinegar and about 1/2 cup EVOO in a food processor. Pulse into a finely chopped herb sauce. If too thick, add another tablespoon of EVOO or vinegar – you want a spoonable sauce.
Boil the potatoes and parsnips until tender. Drain and mash with the soft herb cheese, Parmigiano Reggiano and milk or stock. Season with salt and pepper.
Serve the sliced meat with the mashed potatoes and sliced tomatoes alongside. Top with chimichurri.