Preheat your oven to 400°F and line a baking sheet with parchment paper. Spread the halved cherries over the parchment paper, sprinkle with sugar, and bake them for about 10 minutes until they soften and caramelize slightly. Allow them to cool while you prepare the brownie batter.
Once the cherries are roasted, turn your oven down to 325°F. Spray an 8X8 inch baking pan with non-stick spray, then line the bottom and two sides with parchment paper for easy removal later on. Give it another light spray to ensure nothing sticks.
In a mixing bowl, sift together the flour, cocoa powder, cornstarch, and salt; set this aside as you'll be using it soon.
Using a mixer with a whisk attachment, beat together white sugar, eggs, and egg yolk on high speed for five minutes until it's light and fluffy. While mixing, melt your unsalted butter until just slightly cooled, then add it along with oil and vanilla extract into the sugar-egg mixture on low speed.
Gently remove your mixing bowl from the mixer and add in your sifted dry ingredients into this wet mixture using a rubber spatula; fold them carefully so you don't deflate that lovely air you've created in those eggs.
Fold half of your roasted cherries along with semi-sweet chocolate chips into this brownie batter until well combined before pouring it into your prepared baking pan evenly spread out smooth across all corners.
Bake in your preheated oven for about 40-50 minutes or until edges are set but center remains slightly underdone; top off warm brownies with extra chocolate chips if desired! Let cool completely in pan before freezing briefly for easier cutting—then top off with remaining roasted cherries before serving up this delightful dessert!