Christopher Biggins's secret ingredient (4)
I believe the answer is:
herb
'christopher biggins's secret ingredient' is the definition.
I can't tell whether this definition defines the answer.
'christopher biggins's secret ingredient' is the wordplay.
'ingredient' indicates a hidden word (I've seen 'ingredient of' mean this).
'HERB' is hidden in the letters of 'christopher bigginss secret'.
Can you help me to learn more?
(Other definitions for herb that I've seen before include "Savoury plant" , "Rosemary perhaps" , "Mint possibly" , "'Sage or rosemary, say (4)'" , "Thyme, for example" .)