Cake that’s part of breakfast or tea (5)
I believe the answer is:
torte
'cake' is the definition.
(torte is a kind of cake)
'part of breakfast or tea' is the wordplay.
'part of' says the answer is hidden in the clue.
'TORTE' can be found hidden inside 'breakfast or tea'.
'that's' acts as a link.
(Other definitions for torte that I've seen before include "German cream cake" , "(Austrian) cake with cream and fruit or nuts" , "Rich (Austrian) cake or pastry" , "Sweet cake or tart" , "1d [PASTRY]" .)