Sauce on heat in B&B, say (6,6)
I believe the answer is:
brandy butter
'sauce' is the definition.
(sauce served with Christmas pudding)
'on heat in bb say' is the wordplay.
'on heat' becomes 'randy' (both can mean sexually excited).
'in' indicates putting letters inside.
'say' becomes 'utter' (to utter something is to speak or say it).
'randy' inserted within 'bb' is 'brandyb'.
'brandyb'+'utter'='BRANDY BUTTER'
(Other definitions for brandy butter that I've seen before include "Extra for Christmas pudding" , "Accompaniment to Christmas fare" , "Traditional accompaniment to 5 pudding" , "Sweet companion" , "Fatty alcoholic accompaniment to Christmas pudding" .)