Steps
1. In a small saucepan, combine the unsweetened condensed milk, sugar, cocoa powder, and butter.
2. Cook over medium-low heat, stirring constantly to prevent burning.
3. Continue stirring until the mixture thickens enough to show the pan bottom when scraped (about 10-15 minutes).
4. Remove from heat and let cool to room temperature.
5. Lightly butter your hands, scoop small portions of the mixture, and roll into bite-sized balls.
6. Roll each ball in chocolate sprinkles or shredded coconut if desired.
7. Place brigadeiros on a plate and refrigerate for at least 30 minutes before serving.