In a medium saucepan over low to medium heat, combine the sweetened condensed milk, cocoa powder, and butter. Stir until the butter melts and all ingredients are combined into a smooth mixture.
Continue to stir constantly with a wooden spoon or silicone spatula. The mixture should begin to thicken and bubble. Be careful not to let it stick to the bottom. Cook for about 10-15 minutes, or until the mixture is thick enough to pull away from the bottom of the pan and creates a trail that does not immediately close up when you run the spatula through it.
When the mixture reaches the right consistency, remove it from the heat. Transfer it to a buttered plate and let it cool at room temperature for about 15-20 minutes, or until it is firm enough to handle. To speed up the process, you can place it in the refrigerator for a short time, but not too long to prevent it from hardening.
Grease your hands with a little butter to prevent the mixture from sticking. Scoop a tablespoon of the mixture and roll it into a small ball about 2 cm in diameter.
Place the chocolate sprinkles in a bowl. Roll the balls in the sprinkles until they are completely coated. Place the finished Brigadeiro in small paper cups.
