Duff beer drunk by Simpson, 40% cut with domestic concoction (8)
I believe the answer is:
homebrew
'duff beer drunk by simpson 40% cut' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'with domestic concoction' is the wordplay.
'with' is a charade indicator (letters next to each other).
'domestic' becomes 'home' (similar in meaning).
'concoction' becomes 'brew' (I've seen this before).
'home' put next to 'brew' is 'HOMEBREW'.
Can you help me to learn more?
(Another definition for homebrew that I've seen is " alcohol".)