Slice a raw beetroot thoroughly, and put into the inner pan of a double-pan cooker with a gill of milk. Cover closely and cook for one hour (or longer, if the beet is large); strain the milk, and into a saucepan put half an ounce of butter, half an ounce of flour, and a tablespoonful of proteid food, and the milk in which the beetroot was cooked; stir until it boils. Then add one teaspoonful of red wine vinegar, and return it to the inner pan to warm; then serve.