Sweet thing produced by cook: that's yucky fruitcake (8)
I believe the answer is:
doughnut
'sweet thing' is the definition.
(I know that doughnut is sweet)
'by cook that's yucky fruitcake' is the wordplay.
'by' means one lot of letters go next to another.
'cook' becomes 'do' (do can mean to cook).
'that's yucky' becomes 'ugh' (expression of disgust).
'fruitcake' becomes 'nut' (I've seen this in another clue).
'do' put next to 'ugh' is 'dough'.
'dough'+'nut'='DOUGHNUT'
'produced' acts as a link.
(Other definitions for doughnut that I've seen before include "Sweet cookie" , "Sweet fried snack" , "Small ring-shaped fried cake" , "Ring-shaped object" , "Sweet circular snack" .)