Mar foul mixed recipe (7)
I believe the answer is:
formula
'recipe' is the definition.
(synonyms)
'mar foul mixed' is the wordplay.
'mixed' indicates an anagram.
'mar'+'foul'='marfoul'
'marfoul' is an anagram of 'FORMULA'.
(Other definitions for formula that I've seen before include "One that's on track" , "Set form of words or method" , "Mathematical expression for solving problems" , "Standard rule; recipe" , "Combination of ingredients or symbols" .)