Heat the oven to 220°C/Fan 200°C/Gas 7. Set a large pan of water on to boil. Halve the celeriac and peel it. Slice into chunky chips. Pick off the rosemary leaves and finely chop them.

When the water in the pan is boiling, add the celeriac chips. Bring back to the boil. Simmer for 3 mins.

Drain the celeriac. Spread out on a baking tray. Drizzle with 1 tbsp olive oil. Season. Sprinkle with half the rosemary and a pinch of the chilli flakes (they're spicy, so use as much or as little as you like). Bake for 30 mins till golden brown. Shake half way through.

While the celeriac roasts, peel and grate the garlic in to a shallow bowl. Add the remaining rosemary leaves. Add 1 tbsp sugar and 2 tbsp red wine vinegar. Whisk well with a good pinch of seasoning. Place the steaks into the marinade and set to one side.

Zest the lemon. Add to the half-pot of crème fraîche. Add 1 tbsp each Dijon and wholegrain mustard and 1 tbsp lemon juice. Season well. Taste and add more seasoning or lemon juice if needed.

Slice the mushrooms. Set a frying pan on a high heat. Drizzle 2 tsp olive oil into the pan. Lift the steaks out of the marinade and shake off any excess. Add them to the hot frying pan and fry for 30 seconds on each side for rare steaks. Cook a little longer for a more well done steak. Pop over a plate to rest. Cover with foil.

Add the mushrooms to the frying pan with a pinch of salt and pepper. Stir and fry for 4-5 mins till golden.

Squeeze the remaining lemon into a large bowl. Whisk with 2 tsp olive oil and some seasoning. Toss with the salad leaves.

Add the vinegar marinade from the steaks to the mushrooms. Sizzle for 1 min till bubbling. Serve with the steaks, salad, mustard cream and celeriac chips.