Preheat oven to 400°F. Grease 12 muffin cups (11/4″ x 23/4″) with butter or cooking spray. In a medium microwaveable bowl, microwave chocolate chips and butter, uncovered, on high, 45 to 60 seconds, or until they melt and mixture can be stirred smooth.
In large bowl, beat eggs and egg yolks with wire whisk or electric mixer until foamy. Reserve chocolate syrup pouch from brownie mix. Gradually beat dry brownie mix into egg mixture until well blended. Gently stir in melted chocolate mixture. Fill muffin cups halfway with brownie batter; top each with 1/2 tsp. sprinkles, if desired, then finish off with remaining brownie mixture.
Bake 11 to 14 minutes, or until edges are set. Do not overbake the centers should be soft. Cool 2 minutes in pan.
Loosen each cupcake with knife and invert onto heatproof tray or cookie sheet.
Recipe and photo are from Delish.