This meal is based on the traditional Bistecca alla Fiorentina. The porterhouse steaks are large and cut thick designed to serve two.
Begin by placing the garlic cloves on a wooden chopping board and with the back of your knife, give them a whack. Then, crush the rosemary between your fingers. Place the aromatics into a large, non-reactive dish and mix with olive oil. Lay the porterhouse steaks in the dish and coat evenly with the marinade. Season with plenty of freshly ground black pepper and let marinate for an hour or up to overnight.
If you have an outside grill heat it up until smoking hot. If grilling inside, use a large cast iron griddle/skillet and heat until smoking. Grill the steaks for about 6-7 minutes on each side for medium rare, the traditional* serving temperature. For medium cook for a further 2 minutes per side.
While the steaks are cooking, put the heavy cream in a large sauce pan on medium heat and reduce until it coats the back of a spoon. Add grated nutmeg, grated parmesan and season with salt and freshly ground black pepper. While this is reducing, toss the raw spinach into a food processor. Process until the spinach is the consistency of small flakes, not pureed. Add spinach to reduced cream and stir until fully combined. Shower with additional grated parmesan cheese, to taste.
When you are ready to serve, evenly spread the spinach on top of the steaks, give a squeeze of lemon, a drizzle of extra virgin olive oil and serve with lemon wedges.