Cube of fatty bacon (6)
I believe the answer is:
lardon
'cube of fatty bacon' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lardon that I've seen before include "Strip of bacon for roasting meat" , "bit of a roasting" , "Strip or small cube of fatty bacon" , "Small piece of bacon used in cooking" , "strip of fat" .)