Heat 2 tablespoons oil and gently fry onion until soft. Soak bread cubes in milk for 10 minutes. Put steak, 1 egg, tomato paste, salt and pepper in a bowl and blend well together. Add onion and soaked bread cubes and blend again. Shape mixture into 8 rissoles. Dip in flour, then in remaining egg and coat with breadcrumbs. Heat remaining oil and fry rissoles until well browned on each side. Drain and keep warm. GRA VY: Melt butter in a saucepan and gently fry mushrooms for 2 minutes. Blend in flour and paprika, then stir in stock. Cook gently until boiling, stirring constantly. Remove from heat, stir in sour cream and serve immediately with rissoles. Serves 4.