Authentic Brazilian fudge (Brigadeiro)

1 can sweetened condensed milk
4 tablespoons cocoa powder
1 tablespoon butter
Optional: 1/3 teaspoon vanilla extract
sprinkles to decorate

Mix first four ingredients together in pan.  Stir over medium high heat continuously to avoid burning.  When it starts to stick to the pan and you can scrape it off with a spatula it is ready.  Once it is like a paste consistency, put it in the freezer for an hour to get hard enough so you can roll it into balls.  Make sure your hands are greased well so it won't stick.  Then roll in sprinkles and place on a tray to serve.  Keep in the refrigerator.

I found this recipe here.