Websters lists "handsomest" but I imagine you could use "most handsome" as well.
superlative handsome-most handsomecomparative handsome-more handsome
The comparative and superlative forms of handsome are more handsome and most handsome.
more handsome and most handsome
more handsome, most handsome
most handsome
most handsome
most handsome.
more handsome most handsome
handsomest
Handsomest is already superlative. most handsome
handsomer, handsomest
handsomer, handsomest