Stew at last in bistro? A controversial issue (3,6)
I believe the answer is:
hot potato
'a controversial issue' is the definition.
(I've seen this before)
'stew at last in bistro?' is the wordplay.
'stew' becomes 'hotpot' (I've seen this before**).
'last in' suggests the final letters.
The last letter of 'bistro' is 'o'.
'hotpot'+'at'+'o'='HOT POTATO'
(Other definitions for hot potato that I've seen before include "taken with pinch of salt?" , "Troublesome situation concerning thermal spud" , "Topical, dangerous, issue" , "Controversial and awkward issue" , "Situation likely to cause trouble, like thermal spud" .)