An outing to Carl's rearranged? Well done! (15)
I believe the answer is:
congratulations
'well done' is the definition.
(I've seen this before)
'an outing to carl's rearranged?' is the wordplay.
'rearranged?' indicates an anagram (I've seen 'rearranged' mean this).
'an'+'outing'+'to'+'carls'='anoutingtocarls'
'anoutingtocarls' anagrammed gives 'CONGRATULATIONS'.
(Other definitions for congratulations that I've seen before include "Best wishes" , "Cliff Richard hit" , "praise" , "good show" , "well done" .)