In a medium saucepan, combine the cooked rice, granulated sugar, salt, heavy cream, whole milk, and unsweetened cocoa powder.

Place the saucepan over a low to medium heat, stirring the mixture occasionally to prevent sticking.

Once the mixture begins to boil, reduce the heat to a simmer. Continue to cook for approximately 10 minutes, stirring frequently, until the pudding reaches your desired consistency.

Remove the saucepan from the heat and stir in the unsalted butter until it's completely melted and incorporated.

Allow the pudding to cool for about 5 minutes before serving. If desired, garnish with a dollop of whipped cream or a sprinkle of chocolate shavings.