Variations: Substitute tomahawk steak with boneless ribeye steak or fillet on the bone.
Pre-heat the oven to 200°C/390°F.
Start by making the hasselback potatoes. One at a time, place a potato onto a wooden spoon and make cuts across the width of each potato about 3 to 5mm apart, being careful not to cut all the way through.
Place the potatoes onto a baking tray, drizzle with olive oil and toss to ensure they are evenly coated.
Scatter over thyme sprigs, season with salt and roast in the oven for 40 to 50 minutes, basting regularly with the olive oil or roast until the potatoes are golden and cooked through.
To make the lemon herb butter, add the butter to a bowl, stir in the lemon juice, garlic, parsley, thyme, rosemary, origanum and season to taste with salt. Spoon the mixture into a serving bowl and keep at room temperature for serving.
Lightly coat the tomahawk steak in olive oil and generously rub with salt and freshly ground black pepper. Start cooking the steak about 20 minutes before the potatoes are finished.
Grill the steak on a hot fire or griddle pan, turning to cook on both sides to your preferred doneness; depending on the thickness of the steak, it will take approximately 7 minutes on each side for medium-rare.
Leave the meat to rest for half its cooking time to ensure it is moist, tender and juicy.
Spread the herbed lemon butter over the tomahawk steak and serve alongside the golden roasted hasselback potatoes.