Bread with appropriate side finally covered in unlimited butter (8)
I believe the answer is:
baguette
'bread' is the definition.
(baguette is a kind of bread)
'appropriate side finally covered in unlimited butter' is the wordplay.
'appropriate' becomes 'bag' (I've seen this in other clues).
'finally' suggests the final letters.
'covered in' is an insertion indicator.
'unlimited' indicates the central letters (discard the edges or 'limits' of the word).
The central letters of 'butter' are 'utte'.
The final letter of 'side' is 'e'.
'e' inserted inside 'utte' is 'uette'.
'bag'+'uette'='BAGUETTE'
'with' is the link.
(Other definitions for baguette that I've seen before include "Narrow French stick loaf" , "Bread roll" , "Long loaf - tube gate (anag)" , "Long narrow French loaf" , "Long French breadstick" .)