Whisk the cornstarch, cocoa and sugar in a small saucepan.
Pour the warm milk into the saucepan.
Heat the mixture over medium-low heat, whisking often to avoid lumps.
Bring the hot chocolate mixture almost to a light boil, then reduce the heat to low and fold in the chopped dark chocolate.
Whisk the hot chocolate until thick and creamy, adding more sugar if you like it sweeter.
Divide the Italian hot chocolate among two cups, top with whipped cream and serve.
