Trim the beetroot and put them in a roasting pan with onion, herbs and lemon quarters. Drizzle the olive oil over them and season well with salt and pepper. Cover pan with foil and roast for 2 hours. Leave to cool.

Slip the skins off the beetroot (they should come of easily) and cut the flesh of half the half of them into chunks. Put the chunks in a food processor and process to a puree. Finely chop the remaining flesh and add it to the puree. Season to taste with salt and pepper and add horseradish to taste. Transfer the puree to a saucepan and warm through gently.

Bring a large saucepan of water to the boil and cook the gnocchi according to the instructions on the packet. Remove the gnocchi with a slotted spoon and divide them between 4 warm plates. Top with the beetroot sauce, scatter thyme leaves over each serving and serve.