Son leaves Thomas confused about last Passover biscuit (6)
I believe the answer is:
matzoh
'biscuit' is the definition.
(I've seen this before)
'son leaves thomas confused about last passover' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'leaves' suggests deleting specific letters.
'confused' is an anagram indicator.
'about' is an insertion indicator.
'last passover' becomes 'z' (I can't explain this - if you can you should believe this answer much more).
'thomas' with 's' taken out is 'thoma'.
'thoma' is an anagram of 'matoh'.
'matoh' enclosing 'z' is 'MATZOH'.
Can you help me to learn more?
(Other definitions for matzoh that I've seen before include "Biscuit" , "Passover food" .)