In a medium saucepan, pour in 2 cups of whole milk. Set the heat to medium-low and gently warm the milk, stirring occasionally for about 5 minutes.

Once the milk is warm, add 2 tablespoons of cocoa powder and 2 tablespoons of sugar. Whisk these ingredients together until dissolved.

Stir in the 4 ounces of finely chopped bittersweet chocolate, whisking on medium-low heat until it melts beautifully into the warm milk blend, about 2–3 minutes.

In a small bowl, mix together 1 tablespoon of cornstarch with 1 tablespoon of cold water to create a smooth slurry.

Slowly pour the cornstarch slurry into the hot chocolate while whisking continuously for about 2–3 minutes until it thickens.

Remove from heat and stir in the ½ teaspoon of vanilla extract along with a pinch of salt.

Pour the thick hot chocolate into mugs and top with whipped cream, chocolate shavings, or cocoa powder if desired.