4-letter term for a thick piece of cake, bacon or marble
... 'FLAT, THICK PIECE' is a 15 letter phrase starting with F and 
ending with E ... Large thick slice (of cake etc) (4)  SLAB  Thick mass (4)  SLAB  
Bacon hunk (4)  SLAB  Hunk of meat loaf, say (4)  SLAB  Marble chunk (4)  
SLAB.