I do it mixed with dash of icing (cold and half-baked) (7)
I believe the answer is:
idiotic
'half-baked' is the definition.
(I've seen this before)
'i do it mixed with dash of icing cold' is the wordplay.
'mixed with' is an anagram indicator.
'dash of' indicates taking the first letters (a small amount of the word).
The initial letters of 'icing cold' is 'ic'.
'do'+'it'='doit'
'doit' anagrammed with 'ic' makes 'diotic'.
'i'+'diotic'='IDIOTIC'
'and' acts as a link.
(Other definitions for idiotic that I've seen before include "description of Dostoevsky hero?" , "Senseless" , "Silly" , "Absurd, crackbrained" , "Stupid, foolish" .)