Butchers... back rashers for me. I did start buying stuff in Lidl which is labelled "cooking bacon" - is there another kind? - and sold for €2/kilo... you don't really know what you get i.e. cut, sliced, half-cut, joint, smoked, unsmoked, etc until you open the pack... but I only use that in a coddle... as you're gonna chop it up and trim the fat it doesn't really matter what way it is in the pack.