Direction

1. Prepare the Brownies: Preheat the oven to 350 degrees F (175 degrees C). Line a 13- x 9-inch baking pan with aluminum foil, leaving a 2-inch overhang on short sides. Coat foil and sides of pan with baking spray; set aside.
2. Microwave chocolate and butter in a large microwavable bowl on HIGH, stirring in 30 second intervals, until fully melted and smooth, about 2 minutes total. Whisk in cocoa, canola oil, and vanilla until fully combined.
3. Whisk sugar and brown sugar into chocolate mixture until combined. Add eggs, 1 at a time, whisking until smooth and combined after each addition, about 2 minutes total. Gently fold in flour, cornstarch, salt, and baking powder until just combined, making sure not to overmix the batter, about 45 seconds.
4. Transfer to the prepared baking pan.
5. Bake in preheated oven until set and a wooden pick inserted in the center comes out with a few moist crumbs, 55 to 60 minutes. Remove from the oven and let rest in pan on a wire rack until room temperature, about 1 hour. Once at room temperature, cover, and place in refrigerator; chill completely, at least 1 more hour.
6. When brownie has chilled, prepare the Ganache: Place chocolate in a medium mixing bowl; set aside. Bring heavy cream to a simmer in a small saucepan over medium-high, stirring occasionally. Pour heavy cream over chopped chocolate; whisk until chocolate is fully melted, about 45 seconds. Whisk in butter and salt until smooth and shiny; set aside.
7. Invert cooled Brownie onto a large cutting board and discard aluminum foil. Using a serrated knife, trim and discard outer edges, about 1/4-inch on all sides. Using an offset spatula, spread Ganache in an even layer over top of brownie. Sprinkle evenly with rainbow candy-coated chocolates. Chill Brownie, uncovered, until Ganache is mostly set, about 5 minutes.
8. Cut Brownie into 12 even (4- x 2-inch) pieces. Using the back of the knife, make an indent going crosswise along center of each brownie.