Apply wash to top of granary loaf (5)
I believe the answer is:
glaze
'apply wash' is the definition.
(to glaze something is to apply a wash to it)
'top of granary loaf' is the wordplay.
'top of' suggests taking the first letters.
'loaf' becomes 'laze' (as in to loaf or laze around idly).
The initial letter of 'granary' is 'g'.
'g'+'laze'='GLAZE'
'to' is the link.
(Other definitions for glaze that I've seen before include "Glossy coat" , "Shiny coating" , "Lacquer" , "Pottery coating" , "Glossy surface" .)