Flatten steaks with a meat mallet (or your fist)
Heat 2 tbsp olive oil in frying pan and fry steaks, turning regularly, according to taste.
Meanwhile heat oil in another frying pan and saute onion for three minutes. Add mushrooms and cook for a further two minutes. Add wine and simmer for five minutes. Stir in cream, mustard, tarragon, garlic and seasoning and heat gently to warm through. Serve steaks on a bed of mushroom sauce, garnished with tarragon sprigs.
Note : Steaks should be cooked as follows:Rare - 4 minutes