Attempt to divide open tart and a measure of wine (6)
I believe the answer is:
flagon
'a measure of wine' is the definition.
(amount of wine held by a flagon)
'attempt to divide open tart' is the wordplay.
'attempt' becomes 'go' (go is a kind of attempt).
'to divide' indicates putting letters inside (some letters create a division in others).
'open tart' becomes 'flan' (I've seen this before).
'go' going within 'flan' is 'FLAGON'.
'and' is the link.
(Other definitions for flagon that I've seen before include "Wine jug" , "Red or white container" , "Large rounded bottle, may contain cider" , "Large container for serving drink" , "Large round bottle as for cider" .)