Preheat the oven to 350F and line a 9x9 inch baking pan with parchment paper.
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Whisk in the eggs and vanilla extract.
Fold in the cocoa powder, gluten free flour, cornstarch, and salt until just combined. The batter will be thick.
Spread the batter evenly into the prepared pan. Bake for 20-25 minutes. Do not overbake. Let the brownies cool completely in the pan.
Make the ganache by heating the heavy cream in a small saucepan until just simmering. Pour over the chocolate chips, let sit for 5 minutes, then stir until smooth.
Pour the ganache evenly over the cooled brownies, sprinkle with candy-coated chocolate chips, and chill in the fridge for 1 hour before slicing.