Preheat the oven to 350°F. Line an 8-by-8-inch baking pan with parchment or foil and spray with cooking spray.
Whisk the melted butter, vegetable oil, and both sugars in a large bowl until well combined.
Add the eggs, egg yolk, corn syrup, and vanilla. Whisk until sugar is dissolved and the mixture is creamy, about 5 minutes.
Whisk the cocoa powder, flour, and salt in a small bowl. Then whisk the dry mixture into the wet ingredients, until just combined and no visible streaks of dry ingredients remain.
Transfer the batter to the prepared baking pan. Use an offset spatula to spread the batter into an even layer.
Bake the brownies for 20 to 25 minutes, until the brownies are set, and a toothpick inserted in the center comes out mostly clean.
Let the brownies cool in the pan for 15 minutes then transfer to a wire rack to cool completely.
Make the ganache
Heat the cream in a medium microwave-safe bowl for 30 seconds. Add the corn syrup and stir to combine.
Stir in the chocolate and let sit for 1 minute. Stir once again to combine.
Microwave the mixture in 15-second increments until the chocolate is completely melted, smooth, and shiny, stirring between each heating.
Pour the chocolate ganache over the brownies. Use an offset spatula to spread the ganache in an even layer, covering the entire top of the brownies.
Sprinkle with the Rainbow Crunch Chips.
Refrigerate for 1 to 2 hours, or until the ganache is set, before cutting.
Notes
Brownies can be stored in an airtight container for 3 days at room temperature and for 1 week in the fridge. Brownies are best served chilled.