Chef having bottom pinched: that’s a surprise! (3)
I believe the answer is:
coo
'that's a surprise' is the definition.
(coo is an expression of surprise)
'chef having bottom pinched' is the wordplay.
'chef' becomes 'cook' (I've seen this in other clues).
'having bottom pinched' means to remove the last letter (the last letter is taken away or pinched ).
'cook' with its final letter removed is 'COO'.
(Other definitions for coo that I've seen before include "Gosh!" , "Expression of surprise (by a dove?)" , "Pigeon call" , "crumbs" , "Surprised expression" .)