Make beer, soundly, in the broom cupboard (4)
I believe the answer is:
brew
'make beer' is the definition.
(I've seen this in another clue)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for brew that I've seen before include "Mixture" , "Infuse" , "Concoction" , "Ferment rather than distil" , "Plot" .)