01 - In a medium saucepan, combine the whole milk, heavy cream, cacao powder, granulated sugar, vanilla extract, and sea salt. Whisk vigorously to ensure the cacao powder and sugar are completely dissolved and the mixture is smooth.
02 - Place the saucepan over medium heat, stirring constantly to prevent scorching. Heat the mixture until it is hot and steam begins to rise, but do not allow it to boil. Remove from heat immediately and cover to maintain temperature.
03 - Melt the unsalted butter in a small skillet over medium heat. Add the puffed rice cereal and stir continuously for 1 to 2 minutes until lightly toasted. Remove from the heat, then stir in the chopped dark chocolate until it is fully melted and the cereal is coated. Spread the mixture onto a parchment-lined plate and let cool for 5 minutes to crisp up.
04 - Pour the hot cacao soup into individual serving bowls. Top each serving with a generous spoonful of the crisp chocolate garnish.
05 - Add a dollop of whipped cream and a few fresh berries if desired. Serve immediately to enjoy the contrast between the hot soup and the crisp topping.