Deceive a few about source of mulligatawny soup (8)
I believe the answer is:
consomme
'soup' is the definition.
(consomme is a kind of soup)
'deceive a few about source of mulligatawny' is the wordplay.
'deceive' becomes 'con' (I've seen this in another clue).
'a few' becomes 'some' (both can mean a small amount of something).
'about' indicates putting letters inside.
'source of' suggests taking the first letters (the start - or source - of the word).
The first letter of 'mulligatawny' is 'm'.
'some' placed around 'm' is 'somme'.
'con'+'somme'='CONSOMME'
(Other definitions for consomme that I've seen before include "Clear soup usually of beef, veal or chicken" , "Clear French meat soup" , "Clear meaty soup" , "Thin, clear soup" , "Clear soup made with concentrated stock" .)