In a medium saucepan, combine condensed milk, butter, cocoa powder, and cinnamon over medium heat. Stir often until butter is melted and the mixture is smooth.
Reduce heat to low and continue to cook, stirring constantly, until thickened and pulling from the bottom of the pan, 10-17 minutes. Allow to cool until room temperature or chill in the refrigerator.
Fill a small bowl with cold water. Fill another small bowl with chocolate sprinkles.
Wet your hands and roll about a 1/2 tablespoon size of chocolate into a ball. Coat in chocolate sprinkles and place in a mini paper cup. Repeat with remaining chocolate. Store in the refrigerator for up to 4 days.