• Preheat the oven to 350°F and have ready 9x13" baking dish, lined with nonstick aluminum foil, leaving a bit of an overhang up the sides for easy removal.
• Melt the butter in a microwave-safe bowl or pitcher and set aside until ready to use. 
• In a medium-sized mixing bowl, combine the flour, cocoa powder, and salt. Whisk to combine.
• Add the eggs, the yolk, sugar, and vanilla to a large mixing bowl, and whisk until well combined. Slowly stream in the melted butter, whisking all the while. 
• Add the dry ingredients, and stir to combine with a sturdy wooden spoon. 
• Add the batter to the prepared pan and smooth over the top. Bake for 20-22 minutes, remove from the oven, and allow to cool completely in the pan.

To Make the Ganache:

• Add the heavy cream to a microwave-safe bowl or pitcher and microwave for 30-45 seconds, or until hot.
• Add the chopped chocolate to a small mixing bowl and pour over the hot heavy cream. Allow to sit for about 1 minute.
• Stir the mixture until completely smooth. Add in the corn syrup and stir once more.
• Pour the ganache over the brownies and spread to the edges. Sprinkle the rainbow chip sprinkles across the top and transfer to the refrigerator to set, about 2-3 hours.
• Once set, use the foil overhang to lift the brownies out of the pan and transfer to a work surface. Cut into 16 squares, taking care to remove any foil stuck to the bottom of your brownies, serve and enjoy.