Count a large posh diamond, for example, that's turned up (7)
I believe the answer is:
dracula
'count' is the definition.
(Count Dracula)
'a large posh diamond for example that's turned up' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'diamond for example' becomes 'card' (diamonds is a playing card suit).
'that's turned up' shows that the letters should be reversed in order.
'a'+'l'+'u'+'card'='alucard'
'alucard' backwards is 'DRACULA'.
(Other definitions for dracula that I've seen before include "Blood Count?" , "Fictional count" , "Vampire Count (Stoker)" , "Famous vampire" , "Literary vampire" .)