Amazingly, Adam and Leo are in fashion (1,2,4)
I believe the answer is:
a la mode
'in fashion' is the definition.
(I've seen this before)
'amazingly adam and leo' is the wordplay.
'amazingly' indicates an anagram.
'and' says to put letters next to each other.
'adam'+'leo'='adamleo'
'adamleo' is an anagram of 'A LA MODE'.
'are' acts as a link.
(Other definitions for a la mode that I've seen before include "Fashionable (French)" , "Fashionable in France" , "all the rage" , "In fashion - served with ice cream" , "In the fashion, in Paris?" .)