Season both sides of steak with salt and pepper .

Lay down 4 sheets alfoil, in centre of alfoil place a few slices onion and tomato with a small knob of butter.

Coat one side of steak with whole grain mustard or plain mustard place on onion tomato then coat other side with mustard, butter tomato and onion and wrap tightly so no juice can escape.

Repeat process with each steak till all individually wrapped.

Place seam of alfoil up in s/c on low for 4-5 hrs. Serve with vedies of choice and a gravy