Sweetener for tart in bygone days presented in grand rug (6,5)
I believe the answer is:
golden syrup
'sweetener' is the definition.
(I know that golden syrup is a type of Syrup)
'tart in bygone days presented in grand rug' is the wordplay.
I cannot really understand how this works, but
'bygone' could be 'olden' (I've seen this before) and 'olden' is present in the answer.
'grand' could be 'g' (G is short for grand as in a thousand) and 'g' is present in the answer.
The remaining letters 'syrup' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for golden syrup that I've seen before include "sweetener" , "which could make for sticky situation" , "Light treacle used in 5 down" , "Product of the evaporation of cane sugar juice" , "Sticky, sugary yellow foodstuff" .)