Use milk, endlessly stirred, for cereal (6)
I believe the answer is:
muesli
'cereal' is the definition.
(I've seen this before)
'use milk endlessly stirred' is the wordplay.
'endlessly' means to remove the last letter.
'stirred' indicates an anagram.
'use'+'milk'='usemilk'
'usemilk' with its last letter removed is 'usemil'.
'usemil' anagrammed gives 'MUESLI'.
'for' is the link.
(Other definitions for muesli that I've seen before include "Breakfast food of cereals, dried fruit, nuts etc" , "Oat-based breakfast cereal" , "Grain and dried fruit eaten with milk" , "Breakfast mix of oats, nuts, fruit etc" , "Breakfast mixture of oats, nuts, fruit etc" .)