Multicoloured pastry with fudge filling (4)
I believe the answer is:
pied
'multicoloured' is the definition.
(synonyms)
'pastry with fudge filling' is the wordplay.
'pastry' becomes 'pie' (pie is a kind of pastry).
'with' means one lot of letters go next to another.
'filling' indicates the central letters (the letters which fill the word).
The central letter of 'fudge' is 'd'.
'pie'+'d'='PIED'
(Other definitions for pied that I've seen before include "Foot over water [in]" , "featuring two colours" , "black and white" , "varying in colour" , "Piper thus portrayed once" .)