Mammal eating mammal, a cold dish (7)
I believe the answer is:
cassata
'cold dish' is the definition.
(type of ice cream dish)
'mammal eating mammal a' is the wordplay.
'mammal' becomes 'cat' (cat is a kind of mammal**).
'eating' means one lot of letters goes inside another.
'mammal' becomes 'ass' (ass is a kind of mammal).
'cat' placed around 'ass' is 'cassat'.
'cassat'+'a'='CASSATA'
(Other definitions for cassata that I've seen before include "Ice-cream with fruit and nuts" , "cold dessert" , "Ice-cream dish" , "Neapolitan ice-cream" , "Ice cream containing candied fruit and nuts" .)