Ingredients:

      1 Tbs mustard
      1 tsp sugar
      Salt, black pepper
      1 lb (500 g) mushrooms
      1 lb (500 g) onions
      2 lb (1 kg) fillet of beef
      2 cartons of sour cream

   










     Preparation:

• Mix the mustard with the sugar, one pinch of salt and one tablespoon of hot water into a thick paste and leave to simmer. 
• Wash the mushrooms and slice. 
• Peel and chop the onions. 
• Brown the mushrooms and onions in oil, cover and cook gently for 20 minutes, stirring occasionally. 
• Pour away the liquid. 
• Cut the fillet across the grain into thin slices, dividing these into strips. 
• In another skillet heat the oil on a high temperature and sear the strips of meat in batches. 
• Turn and brown on all sides, using a slotted spoon to transfer the meat to the mushrooms in the other skillet. 
• Season with salt and pepper, mix in the mustard paste and stir in the sour cream. 
• Cover and heat, stir and serve.