Reserve ½ cup of whole milk in a small bowl for later use.

In a medium saucepan, combine 3.5 cups of whole milk, ¼ teaspoon salt, 3 tablespoons unsweetened cocoa powder, and ¼ cup granulated sugar. Heat on medium while stirring until it simmers (4-5 minutes).

Add 3.5 oz. of chopped dark chocolate to the simmering mixture, stirring continuously until fully melted (2-3 minutes).

Mix 1 tablespoon of cornstarch with the reserved milk until dissolved to create a slurry.

Gradually pour the cornstarch slurry into the saucepan while whisking. Cook for 1-2 minutes until thickened.

Remove from heat and stir in 1 teaspoon of vanilla extract until well combined.

Pour into mugs and serve warm, optionally garnished with chocolate shavings or marshmallows.