In a nonstick heavy saucepan, heat the condensed milk, cocoa and 2 tablespoons butter to boiling, stirring constantly with wooden spoon. Reduce heat to medium-low; cook 10 to 15 minutes, stirring constantly, until mixture is thick and shiny and starts to pull away from bottom and side of saucepan when pan is tilted. Mix in the vanilla extract.
Pour mixture into greased shallow pan and cool completely (refrigerate to firm up faster).
While cooling chop nuts if your grocery store was like mine and didn’t have any already chopped.
Use teaspoon or melon baller to scoop cooled mixture, then use greased hands to shape into 1- to 1 1/2-inch balls.
Pour toppings into separate bowls.
Roll each ball in pistachios, almonds, coconut or sprinkles and place in mini paper baking cups.