1. To make the celeriac purée, place the celeriac and potatoes in a steamer over simmering water and steam for 20 minutes. Add the apple and steam for a further 10 minutes. Remove when they are soft. Pass the celeriac, potato and apples through a food mill, or press through a sieve. Place in a bowl and slowly stir in the extra virgin olive oil, lemon juice, salt and pepper. Keep warm.

2. To make the herb salad, pick and wash the salad leaves and herbs, spin dry or dry on a tea towel. Combine and refrigerate.

3. To make a dressing for the salad, mix the extra virgin olive oil and the lemon juice together, season and stir. Set aside.

4. Season the fish to taste. Place a heavy cast-iron pan large enough to fit the 4 steaks on medium heat. Add oil, butter and thyme. As soon as this starts to foam add the swordfish steaks and cook, spooning the foaming butter over the fish from time to time. Cook for about 4 minutes, until golden brown. Turn, cooking for a further 4 minutes until golden brown. Cook a little longer if you don't want the fish medium-rare. 

5. Place the salad leaves in a serving bowl and add the dressing.

6. Spoon the celeriac purée onto four plates, top with swordfish, then spoon the thyme-flavoured burnt butter over the fish and garnish with the thyme sprigs. Serve with the herb salad and lemon wedges.