Pour 2-3 cups of whole milk and ½ cup of heavy cream into a medium-sized heavy-bottomed saucepan. Heat over medium heat until it starts to steam, avoiding boiling.

In a small bowl, whisk together ½ cup cocoa powder and 1-2 tablespoons of grated chocolate. Add about ½ cup of the hot milk mixture to this bowl and whisk until smooth.

Slowly pour the chocolate mixture back into the saucepan while whisking constantly. Add the entire can of sweetened condensed milk and ⅛ teaspoon of vanilla extract, whisking until well mixed.

Reduce the heat to low and let it simmer for 3-5 minutes, stirring frequently until thickened.

Ladle the hot chocolate into heat-resistant mugs. Top with whipped cream and a sprinkle of ground cinnamon, adding chocolate shavings if desired. Serve hot.