Cold sweets oddly increase (4)
I believe the answer is:
ices
'cold sweets' is the definition.
'ices' can be an answer for 'sweets' (ice is a kind of sweet). I am unsure of the 'cold' bit.
'oddly increase' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternating letters of 'increase' are 'ICES'.
Can you help me to learn more?
(Other definitions for ices that I've seen before include "ecorates with frosting" , "Freezes" , "summer refreshment" , "Decorates cake with sugar topping" , "Decorates cakes with frosting" .)