Topping in cake is not gooey, initially (5)
I believe the answer is:
icing
'topping' is the definition.
(icing is a kind of topping)
'in cake is not gooey initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'in cake is not gooey' is 'ICING'.
(Other definitions for icing that I've seen before include "Cake-topper" , "Sugar preparation" , "Sweet cake topping" , "in the freezer?" , "Maybe Madeira's topping" .)