Potatoes softly immersed in lather (5)
I believe the answer is:
spuds
'potatoes' is the definition.
(spud can informally mean potato)
'softly immersed in lather' is the wordplay.
'softly' becomes 'p' (short for piano, musical term for softly).
'immersed in' indicates putting letters inside.
'lather' becomes 'suds' (synonyms).
'p' going into 'suds' is 'SPUDS'.
(Other definitions for spuds that I've seen before include "Potatoes (colloq.)" , "Potatoes (informal)" .)