Potato chips ultimately followed by dessert (4)
I believe the answer is:
spud
'potato' is the definition.
(I've seen this before)
'chips ultimately followed by dessert' is the wordplay.
'ultimately' indicates one should take the final letters.
'followed by' means one lot of letters go next to another.
'dessert' becomes 'pud' (pud is a kind of dessert).
The final letter of 'chips' is 's'.
's'+'pud'='SPUD'
(Other definitions for spud that I've seen before include "Commoner's King Edward?" , "Tattie" , "Potato (informal)" , "King Edward, e.g." , "The common potato" .)