Cup of tea and large dessert (7)
I believe the answer is:
chalice
'cup' is the definition.
(chalice is a kind of cup)
'tea and large dessert' is the wordplay.
'tea' becomes 'cha' (cha is a type of tea).
'and' means one lot of letters go next to another.
'large' becomes 'L' (eg in clothes sizes).
'dessert' becomes 'ice' (ice is a kind of dessert).
'cha'+'l'+'ice'='CHALICE'
'of' acts as a link.
(Other definitions for chalice that I've seen before include "Large goblet for consecrated wine" , "Necessity for communion" , "Sacred cup for consecrated wine" , "Cup used in church" , "cup used in company with host" .)