Flipping excellent mushrooms eaten by the French in particular (8)
'particular' is the definition.
'flipping excellent mushrooms eaten by the french' is the wordplay.
'flipping' is a reversal indicator.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'mushrooms' becomes 'ceps' (I've seen this before).
'eaten by' is an insertion indicator.
'the french' becomes 'le' ('the' in French).
'aiceps' placed inside 'le' is 'laicepse'.
'laicepse' written backwards gives 'ESPECIAL'.
'in' is the link.
(Other definitions for especial that I've seen before include "Spice ale wrongly and be particular", "Unusual", "Over and above what is usually expected", "Notable; for one person or thing only", "Exclusive".)