Biscuit barrel turned up, overlooked by Sandy?
I believe the answer is:
ginger nut
'biscuit' is the definition.
(I've seen this before)
'barrel turned up overlooked by sandy?' is the wordplay.
'barrel' becomes 'tun' (tun is a kind of barrel).
'turned up' is a reversal indicator.
'overlooked by' says to put letters next to each other (in a down clue, some letters go above others).
'sandy?' becomes 'ginger' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'tun' back-to-front is 'nut'.
'nut' after 'ginger' is 'GINGER NUT'.
Can you help me to learn more?
(Other definitions for ginger nut that I've seen before include "redhead?" , "Kind of biscuit" , "Type of biscuit" , "Variety of biscuit" , "Spicy biscuit" .)