Method

1. Place the potato chunks into a large pan of cold salted water, bring to the boil, then reduce to a simmer. Cook for 15-20 minutes until tender when pierced with a knife.
2. While the potatoes are cooking, prepare the cavolo nero by stripping the leaves from the tough central stems and discarding the stems. Roughly chop the leaves and wash thoroughly.
3. Remove your steak from the fridge 10-15 minutes before cooking to bring it to room temperature. Pat dry with kitchen paper.
4. When the potatoes are nearly done, blanch the cavolo nero. Bring a separate pan of salted water to the boil, add the leaves and cook for 3-4 minutes until tender. Drain well and set aside.
5. Heat a dry cast iron or stainless-steel frying pan over high heat. Coat the steak generously with olive oil on both sides and season well with salt and pepper.
6. Once the pan is very hot, add ½ tablespoon of olive oil followed by the steak. Cook for 2 minutes on each side for medium rare or adjust timing to your preference. Transfer to a warm plate, cover with foil and leave to rest for 10 minutes.
7. Drain the potatoes and return to the pan. Add butter and a splash of milk, then mash until smooth and creamy. Season to taste and keep warm.
8. Heat a drizzle of olive oil in a frying pan, add the cavolo nero with a crushed garlic clove if desired, and sauté for 2-3 minutes. Season with salt and pepper.
9. Wipe the pan you used to fry the steak with kitchen paper and place on a low heat. Add 2 tablespoons of olive oil, the finely sliced garlic, rosemary and sage leaves. Continually stir for about 30 seconds, until the garlic starts to colour.
10. Slice the rested steak across the grain into long thin strips and set alongside the mash potato and cavolo nero, spooning the oil, garlic, rosemary and sage mix over the steak and adding a squeeze of lemon to finish.