Odd bits from that poison chap’s pudding ingredient (7)
I believe the answer is:
tapioca
'pudding ingredient' is the definition.
(I've seen this in another clue)
'odd bits from that poison chap's' is the wordplay.
'odd bits from' means one should take alternating letters (letters in odd-numbered positions).
'that'+'poison'+'chap'='thatpoisonchap'
The alternate letters of 'thatpoisonchap' are 'TAPIOCA'.
(Other definitions for tapioca that I've seen before include "Starchy white substance used to make puddings" , "it thickens" , "Starchy pudding" , "Starch from cassava used in making puddings" , "Starchy dish" .)