Pour the sweetened condensed milk and chocolate into a small saucepan over medium-high heat.
Stirring constantly, cook the sweetened condensed milk until thickened.
Pour the cooked sweetened condensed milk into a wide, shallow dish and let it cool.
When the sweetened condensed milk has cooled, rub a small amount of butter on your hands and then roll the sweetened condensed milk into small balls. Roll each ball into cocoa powder.
