In a medium saucepan, combine the sweetened condensed milk, cocoa powder, and unsalted butter.
Cook over medium heat, stirring constantly to prevent burning.
Continue cooking until the mixture thickens and starts to pull away from the sides of the pan, about 10-15 minutes. It should be thick enough to hold its shape when scooped.
Remove the saucepan from the heat and stir in the vanilla extract if using.
Transfer the mixture to a plate or dish and let it cool to room temperature.
Once the mixture has cooled and is firm enough to handle, lightly grease your hands with butter or oil.
Scoop out small portions of the mixture and roll them into small balls, about 1 inch in diameter.
Roll each ball in chocolate sprinkles or your choice of coating until fully covered.
Place the coated brigadeiros in paper cups or on a serving plate.
Enjoy your meal!