Urge VIP to tuck into stock food: it's sweet stuff (3,7)
I believe the answer is:
egg custard
'sweet stuff' is the definition.
(sweet food)
'urge vip to tuck into stock food' is the wordplay.
'urge' becomes 'egg' (as in egging someone on).
'vip' becomes 'star' (both can mean an important or famous person).
'to tuck into' means one lot of letters goes inside another.
'stock food' becomes 'cud' (regurgitated food chewed again by a ruminant).
'star' inserted inside 'cud' is 'custard'.
'egg'+'custard'='EGG CUSTARD'
'it's' is the link.
(Other definitions for egg custard that I've seen before include "Baked dish" , "Baked dessert or yellow pouring sauce" .)