Preheat grill and oven: Preheat your grill on high heat and your oven to 190°C (375°F).
Season the steak: Generously season both sides of the Tomahawk steak with salt and cracked black pepper. Drizzle olive oil on both sides and rub it in.
Sear the steak: Place the steak on the hot grill and sear for 3 to 4 minutes on each side until a nice crust forms.
Insert temperature probe: Insert a wireless digital thermometer probe into the thickest part of the steak to monitor internal temperature.
Finish cooking in oven: Transfer the steak to a tray lined with baking paper and place it in the preheated oven. Cook until the internal temperature reaches 60°C (140°F) for medium rare, about 40-50 minutes.
Prepare garlic butter: While the steak is cooking, melt garlic butter in a small saucepan to serve with the steak.
Rest the steak: Remove the steak from the oven and let it rest for 5 minutes before slicing.
Slice and serve: Using a sharp knife, slice the steak across the grain. Serve with skin-on chips and drizzle with melted garlic butter.