In a small bowl, whisk the cornstarch with ¼ cup of the milk until completely smooth, creating a slurry. Set aside.
In a small saucepan over medium heat, add the remaining milk, cocoa powder, sugar, and salt. Whisk well until fully combined.
Warm the mixture until steaming but do not let it boil.
Add the chopped dark chocolate and stir until melted and smooth.
Whisk in the cornstarch slurry and continue cooking, stirring constantly.
Cook for 2–4 minutes, until the hot chocolate thickens to a rich, velvety, spoon-coating consistency.
Remove from heat and stir in vanilla or citrus zest, if using.
Serve immediately in small cups, just as it’s enjoyed in Italian cafés. Optional top with fresh whipped cream.
