Remove the stalks and leaves from the beetroot and plunge them into a bowl of cold water. Give them a good wash to remove any grit, drain and rinse again. then set aside to dry. Wash the whole beetroot, scrubbing well to remove any dirt. Pat dry, then place in the centre of a square of foil, season, coat with 1 tbsp of the oil and wrap. Cook in the air-fryer at 200C for 50 mins or in the oven at 220C/200C fan/gas 7 until a sharp knife pierces through it easily. Set aside to cool before finely slicing.

Meanwhile, pour the vinegar, sugar and coriander seeds into a saucepan with 1 tsp salt. Bring to a simmer, then remove from the heat. Add the beetroot stalks, reserving the leaves. Stir and set aside to pickle for at least 30 mins. Combine the horseradish, soured cream, 1 tsp of honey and a splash of the lemon juice. Season, adding more horseradish if you like. Keep chilled until needed.

Put the mustard in a large bowl with the remaining lemon juice and honey, mint and the remaining oil. Whisk together and season, then stir in the lentils and beetroot leaves. Roughly chop some of the pickled beetroot stalks before stirring in. Spread the lentil mixture over a platter, top with the beetroot, fish, if using, and horseradish cream to serve.