COMBINE sweetened condensed milk and cocoa in medium saucepan. Cook over medium-low heat, stirring constantly, for about 10 to 15 minutes or until mixture pulls away from the sides of the pan. Remove from heat. Add butter and salt; mix thoroughly. Let cool for 20 minutes.
LINE baking sheet with wax paper. Using teaspoon, drop 1-inch dollops of chocolate mixture onto prepared baking sheet. Refrigerate for 30 minutes. Spray hands with cooking spray. Shape or roll chocolate mixture into balls and then roll in sprinkles. (Hands may need to be resprayed while rolling). Keep refrigerated in airtight container for up to 5 days.