Peel the kohlrabi and cut into small pieces. Melt the margarine and stir in the flour. Add the milk, cream and water while stirring. Season to taste with the instant stock. Add the kohlrabi and simmer for about 10 minutes until the vegetables are soft.
Clean and wash the cress and add to the soup.
Remove the soup from the stove and puree. Season with salt, pepper and lemon juice.
Dice the toast and brown in hot fat. Serve the soup with the croutons and sprinkle with chilli flakes if necessary.