Rub steaks with salt & pepper and leave at room temperature for at least 30 minutes before cooking. Or, place steaks on a plate in the refrigerator for up to 24 hours.

Rub 1-2 tsp of avocado oil (or olive oil) over each steak.

Heat a dry cast iron skillet on the grill rack for at least 15 minutes while your grill preheats. If you are using a non-gas grill, set up two heating zones: one for high heat, and a separate zone for low heat. You know the skillet is ready when you splash water on the skillet and it sizzles.

Add the oiled steaks to the dry, hot skillet. It will smoke. Allow steaks to sear for 2-3 minutes, until you have a very dark brown sear. Flip the steak with the tongs and sear the other side for about 2-3 minutes until it is nice and brown. Keep the lid open.

Turn the heat down to low (or move your steak to the low-heat zone). Cook until you reach the desired temperature, about 5 minutes for medium to rare steak. See notes. Remove steak and cover with foil, wait 15 minutes before slicing against the grain to serve.

Over medium heat, melt 2 Tbsp butter and 1 Tbsp avocado oil. Add shallots and garlic and saute until browned about 2 minutes. Add heavy whipping cream and simmer until it starts to thicken. Add Worcestershire, mustard, and salt & pepper to taste. Simmer until the sauce starts to bubble.

Serve cream sauce over sliced steak and garnish with chopped parsley.