Combine Ingredients: In a medium saucepan, combine the sweetened condensed milk, unsweetened cocoa powder, and butter.

Cook the Mixture: Cook over medium heat, stirring constantly, until the mixture starts to thicken and pull away from the sides and bottom of the pan. This should take about 10-15 minutes. The mixture is ready when you can see the bottom of the pan while stirring.

Add Vanilla: Remove the saucepan from the heat and stir in the vanilla extract.

Cool the Mixture: Transfer the mixture to a plate or shallow dish and let it cool to room temperature. You can also refrigerate it for about 30 minutes to make it easier to handle.

Form the Brigadeiros: Once the mixture is cool, butter your hands lightly to prevent sticking. Scoop out small portions of the mixture and roll them into balls about the size of a walnut.

Roll in Sprinkles: Roll each ball in chocolate sprinkles until fully coated.

Serve: Place the brigadeiros in mini paper liners for a nice presentation. Store them in an airtight container at room temperature or in the refrigerator.