Old woman’s hot potato dish (4)
I believe the answer is:
mash
'potato dish' is the definition.
(mashed potato)
'old woman's hot' is the wordplay.
'old woman's' becomes 'ma's' (belongs to ma).
'hot' becomes 'h' (abbreviation eg on taps).
'mas'+'h'='MASH'
(Other definitions for mash that I've seen before include "(Crush into) pulp" , "Creamed potatoes" , "Pureed potatoes" , "Animal feed" , "Pummel" .)