Course designers ultimately admitted to waste (7)
I believe the answer is:
Here is my best explanation:
'course' is the definition.
(dessert is a kind of course)
'designers ultimately admitted to waste' is the wordplay.
'ultimately' indicates one should take the final letters.
'admitted to' means one lot of letters goes inside another.
'waste' becomes 'desert' (a desert may be described as a wasteland).
The final letter of 'designers' is 's'.
's' inserted inside 'desert' is 'DESSERT'.
(Other definitions for dessert that I've seen before include "Last course, sweet", "tart?", "end", "End of meal", "Pudding, sweet", "Spotted Dick is one", "Fool possibly", "Charlotte maybe", "Fruit and nuts, perhaps" and "Christmas pudding maybe".)