1) Flatten your steaks a little with a meat mallet ot a rolling pin. 2) Put 2 tbsp oil into a hot frying pan and fry turning regularly, according to taste. 3) Meanwhile heat remaining oil in another frying pan and sauté onion for 3 minutes. 4) Add mushrooms and cook for a further 2 minutes. 5) Add wine and simmer for 5 minutes. 6) Stir in cream, mustard, tarragon, garlic and seasoning and heat gently to warm, do not boil. 7) Serve steaks with sauce poured over.