Preheat your oven to 400°F. Line a baking sheet with parchment paper and spread the cherry halves out in a single layer. Sprinkle lightly with sugar. Roast for 10 minutes, then allow to cool. This step concentrates their sweetness and adds a slight caramelized flavor.

Reduce the oven temperature to 325°F. Lightly spray an 8x8-inch square pan with baking spray. Line the bottom and two sides with parchment paper, leaving an overhang for easy removal, then spray again.

In a bowl, sift together the flour, cocoa powder, cornstarch, and salt. Set aside.

In a stand mixer fitted with the whisk attachment (or using a hand mixer), beat the sugar, eggs, and egg yolk on high speed for 5 minutes. This step helps create a light, glossy texture and crackly top.

While the eggs are beating, melt the butter and allow it to cool slightly. Add the butter, oil, and vanilla to the egg mixture. Mix on low speed until just incorporated.

Remove the bowl from the mixer. Gently fold in the dry ingredients with a rubber spatula, being careful not to deflate the airy batter.

Reserve half of the roasted cherries for topping. Gently fold the remaining cherries and chocolate chips into the batter until evenly distributed.

Pour the batter into the prepared pan and spread it evenly. Bake for 40–50 minutes. The edges should be set while the center remains slightly soft—this ensures a fudgy texture. Let cool completely in the pan.

Once cooled, place the pan in the freezer for 15 minutes. This helps the brownies set and makes slicing easier. Remove from the pan, top with the remaining roasted cherries, slice, and serve.