Preheat the oven to 400°F. Line a baking sheet with parchment paper. Spread the cherry halves in a single layer on the sheet and sprinkle with the 1 tablespoon of sugar. Roast for 10 minutes, then remove from oven and let cool completely on the sheet.

Reduce the oven temperature to 325°F. Grease an 8x8-inch baking pan with nonstick spray, then line the bottom and two opposite sides with a parchment sling, leaving overhang. Spray the parchment again.

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

In a large mixing bowl, using an electric mixer with the whisk attachment, beat the 1 1/3 cups sugar, whole eggs, and egg yolk on high speed for 5 minutes, until thick and pale.

With the mixer on low, add the melted butter, oil, and vanilla, mixing just until combined. Remove the bowl from the mixer. Gently fold in the dry ingredients with a rubber spatula, taking care not to deflate the batter.

Reserve half of the cooled roasted cherries for topping. Fold the remaining half of the cherries and 3/4 cup of the chocolate chips into the batter until evenly distributed. Pour the batter into the prepared pan and spread into an even layer.

Bake for 40 to 50 minutes, until the edges are set and a toothpick inserted near the center comes out with moist crumbs. The center should still look slightly underdone. Immediately sprinkle the remaining 1/4 cup chocolate chips on top. Let the brownies cool completely in the pan on a wire rack.

Once cool, place the pan in the freezer for 15 minutes to make slicing easier. Use the parchment sling to lift the brownies out of the pan. Top with the reserved roasted cherries, then cut into 16 squares and serve.