Mollusc served with soft pile of potatoes? (5)
I believe the answer is:
clamp
'pile of potatoes?' is the definition.
(heap of potatoes or other vegetables)
'mollusc served with soft' is the wordplay.
'mollusc' becomes 'clam' (clam is a kind of mollusc).
'served with' is a charade indicator (letters next to each other).
'soft' becomes 'p' (musical abbreviation for 'piano'**).
'clam'+'p'='CLAMP'
(Other definitions for clamp that I've seen before include "Wheel vice" , "Pile of bricks" , "Grip firmly" , "Firmly press" , "device to hold" .)