Cover a plate with plastic wrap and set aside. In a saucepan, whisk together the condensed milk and cocoa powder. Add the heavy cream and mix well. Add butter.
Cook over medium heat, stirring constantly for about 20 minutes, or until it reaches 210 - 215 °F (or when the mixture thickens and pulls away from the sides of the pan easily). Remove from heat and continue mixing for 1 more minute. Pour the truffle mixture onto the plastic wrapped plate. Use another piece of plastic wrap to cover the mixture and let it cool down completely at room temperature (about 1-2 hours). It can be stored in the refrigerator for up to 1 week, but the mixture has to be at room temperature before making the balls.
To make 1 ½ inch balls, use a teaspoon or melon baller to scoop the truffle mixture. Use greased hands to shape the balls. Roll each ball in sprinkles and place them in mini paper baking cups.
Recipe reprinted with permission © 2021 Aryane Mendes Andrade Oar