In a frying pan large enough to take the 4 slices of liver, melt the butter and when it is foaming add the liver and cook until medium cooked, turning once. Season with salt and freshly ground black pepper.
Remove the liver from the pan, add the sultanas, tomato coulis, port and brandy. Mix well together to make a smooth sauce. Check the seasoning.
Serve the liver with the sauce poured over it.