Defrost the beef until room temperature, marinade the meat with chopped rosemary(or use dry one). Rub with olive oils, sea salt and ground pepper

Heat up iron or pan until it get some smoke. The pan needs to be very hot. Grill the steak with high heat. Each side for 2 minutes

Before finished grilling, put butter on top and let it melt into steak. Then rest the steak on the cutting board for 3 minutes

For bell peppers, use the same pan, put olive oil. Wait until pan is warm. Stir fry until bell peppers are soft.

Season bell peppers with salt and ground peppers

Serve steak and bell peppers with mustard sauce