Pour 2-3 cups whole milk and ½ cup heavy cream into a medium-sized heavy-bottomed saucepan. Heat over medium heat until steaming with tiny bubbles around edges, but do not boil.
In a small bowl, whisk together ½ cup cocoa powder and 1-2 tablespoons grated chocolate. Add about ½ cup hot milk mixture and whisk until smooth.
Slowly pour chocolate mixture back into saucepan while whisking constantly. Add entire can of sweetened condensed milk and ⅛ teaspoon vanilla extract. Whisk until combined and smooth.
Reduce heat to low and simmer for 3-5 minutes, stirring frequently, until thickened enough to coat the back of a spoon. Adjust thickness with more milk if needed.
Ladle hot chocolate into mugs. Top with whipped cream, a sprinkle of ground cinnamon, and chocolate shavings if desired. Serve hot for an authentic Disney park experience.
