Hot beetroot soup

• 1 lb (450 g) fresh beetroots
• 1 large potato
• 1

Peel the skins from the beetroot and potato, then cut them in even-sized chunks. Peel and finely chop the onion. Melt the butter in a large saucepan over low heat, add the onion and fry gently for 5 minutes to soften but not brown. Stir in the stock, season with salt and pepper and bring to the boil. Add the beetroot and potato, lower the heat, and cook gently, covered, for 40 minutes until veg