Mother's heading in to make a meal (5,3)
I believe the answer is:
cream tea
'meal' is the definition.
(I've seen this before)
'mother's heading in to make a' is the wordplay.
'heading' says to take the initial letters (head could mean the top letter).
'in' means one lot of letters goes inside another.
'to make' becomes 'create' (creating is a kind of making).
The first letter of 'mothers' is 'm'.
'm' inserted within 'create' is 'creamte'.
'creamte'+'a'='CREAM TEA'
(Other definitions for cream tea that I've seen before include "tasty treat" , "Afternoon meal - macerate (anag)" , "afternoon treat" , "snack" , "calorie-packed meal" .)