In a medium saucepan, pour in the whole milk and heavy cream. Place over medium heat, stirring occasionally until steaming but not boiling, about 3 minutes.

While the milk heats, take a small bowl and combine the high-quality cocoa powder and grated milk chocolate. Once the milk is steaming, add ½ cup of this hot milk mixture to the bowl and whisk until you achieve a smooth paste.

Gradually whisk the chocolate mixture back into the saucepan with the remaining milk. Then, add in the sweetened condensed milk and vanilla extract, stirring continuously until well combined.

Lower the heat and allow the mixture to simmer gently for about 5 minutes, stirring frequently. This will thicken the hot chocolate.

Once thickened, remove saucepan from heat. Ladle hot chocolate into mugs, topping with whipped cream and a sprinkle of ground cinnamon. Serve immediately.