Buy about fifty pounds of beef? (5)
I believe the answer is:
bully
'beef?' is the definition.
(bully beef is a kind of beef)
'buy about fifty pounds' is the wordplay.
'about' is an insertion indicator.
'fifty' becomes 'l' (roman numeral).
'pounds' becomes 'l' (L can represent the monetary pound).
'l'+'l'='ll'
'buy' going around 'll' is 'BULLY'.
'of' acts as a link.
(Other definitions for bully that I've seen before include "excellent" , "Intimidate" , "Very good" , "Flashman, say" , "Beef cured or pickled in brine" .)