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 know nothing about this answer so I can't tell whether this works.
'with domestic concoction' is the wordplay.
'with' means one lot of letters go next to another.
'domestic' becomes 'home' (similar in meaning).
'concoction' becomes 'brew' (I've seen this in another clue).
'home' put next to 'brew' is 'HOMEBREW'.
Can you help me to learn more?
(Another definition for homebrew that I've seen is " alcohol".)