Finely grate the zest from the lemon. Juice it. Fill the kettle and boil it.
Fill a pan with hot water from the kettle. Add the lemon juice. Rinse and peel the Jerusalem artichokes (but don't worry about the odd bit of skin). Chop. Add to the pan. Peel and chop the potatoes. Add them. Cover. Boil for 15-20 mins till tender.
Peel and slice the shallots. Trim, rinse and shred the cavolo nero. Put to one side.
Drain the artichokes. Mash with a fork on top of the hob to dry them out then mash in the butter and half the lemon zest. Taste and season. Cover and put to one side.
Measure out 1 tsp of the cumin seeds. Toast in a dry frying pan for 2-3 mins till fragrant. Tip into a bowl.
Warm a splash of olive oil in the frying pan. Add the shallots. Cook the shallots over a lowish heat for 5-10 mins till soft and glossy but still pale. Lift out of the pan. Put to one side.
Turn up the heat under the frying pan. Season the steaks with salt and pepper. Add to the pan. Fry for 1-2 mins each side. Pop the steaks on a plate. Rest, covered in foil.
Add the cavolo nero to the pan. Stir the shallots back in with 100ml hot water from the kettle. Stir fry for 4-5 mins till wilted and the water has evaporated. Serve with the steaks and artichoke smash, topped with the toasted cumin seeds and the rest of the lemon zest.