In a mixing bowl, combine heavy whipping cream, 2 tablespoons cocoa powder, and powdered sugar. Whip with an electric mixer on high speed until stiff peaks form, about 3-4 minutes. Refrigerate until ready to use.

In a medium saucepan, heat the milk over medium heat until it begins to steam but not boil, about 3-4 minutes.

Reduce heat to low and whisk in the remaining 2 tablespoons cocoa powder, granulated sugar, chopped dark chocolate, and salt. Stir continuously until the chocolate is completely melted and the mixture is smooth.

Remove from heat and stir in vanilla extract. Whisk vigorously for 30 seconds to create a frothy texture.

Pour the hot chocolate into mugs, filling them about three-quarters full.

Generously dollop the whipped cocoa cream on top of each mug. The cream will slowly melt into the hot chocolate. Serve immediately and enjoy while hot.