Start by making the masala by frying off the onion in the rapeseed oil on a medium heat till golden brown. Next add the garlic, ginger and chill and fry for 1 minute. The garlic and ginger will give a great aroma of power and kick to the dish. Now add the tumeric, cumin for added punch, peppercorns and fry for a further 30 seconds. Add the chopped tomatoes for a bit of sweetness, beef stock cube and 300ml of water. Cook until the oil splits out of the spices into the sauce. Once this happens, remove from the heat, season with salt and whisk in the 100g of butter and the chopped coriander ready to serve.
To prepare the potatoes, peel and cut into roughly 2.5cm/1in chunks. Put the potatoes in a pan and cover with cold water. Bring to the boil, reduce the heat slightly and simmer for 5 minutes.
Drain the potatoes in a colander and leave to stand for 2 minutes. Bash up the edges of the potatoes a little by shaking the colander from side to side. This will help make them extra crisp.
Melt the butter with the oil in a large non-stick frying pan or sauté pan. Tip the potatoes into the pan and season with salt and plenty of freshly ground black pepper. Fry over a medium-low heat for 10 minutes, stirring occasionally.
Open out the garlic bulb and remove the cloves. Scatter the unpeeled garlic cloves into the pan with the potatoes and cook for 15 minutes, turning regularly until the potatoes are golden-brown all over and the garlic has softened. Sprinkle over the coriander leaves and cook for 5 minutes more, stirring and turning the potatoes as before. Once the coriander has been added to the potatoes, the steaks can be cooked.
Once the steak is cooked to your liking and rested, place on a warm serving plate with the golden crispy potatoes and that amazing pepper masala drizzled over half the steak.