Turning up with diamonds and ring -- that's sweet (7)
I believe the answer is:
pudding
'that's sweet' is the definition.
(pudding is a kind of sweet)
'turning up with diamonds and ring' is the wordplay.
'turning' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'diamonds' becomes 'd' (abbreviation in bridge say).
'and' says to put letters next to each other.
'ring' becomes 'ding' (dinging is a kind of ringing).
'up' written backwards gives 'pu'.
'pu'+'d'+'ding'='PUDDING'
(Other definitions for pudding that I've seen before include "Chubby person" , "Pease - -" , "Sweet course" , "Cooked sweet dish" , "Dessert course" .)