Put the vegetables (beetroot, celery, potatoes, carrots) in a large saucepan and add enough vegetable stock to cover 2-3 cm.
Bring the soup to the boil and add the apples after about 10 minutes.
Let the soup simmer on a low level with the lid closed until the vegetables are soft (this took me about 45 minutes and depends on the size of the pens).
Cool the soup a little and add the cream (if the soup is too hot, the cream will curdle). Season with salt and pepper if necessary. Sprinkle with herbs before serving.