Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper and spread the halved cherries evenly across it. Sprinkle sugar over the cherries and roast them in the oven for 10 minutes.

After removing the cherries from the oven, reduce the oven temperature to 325°F (160°C). Spray an 8x8 inch baking pan with non-stick spray and line it with parchment paper.

In a large mixing bowl, sift together the all-purpose flour, Dutch process cocoa powder, cornstarch, and salt. Set this bowl aside.

In a separate bowl, beat together the granulated sugar, eggs, and egg yolk on high speed for about 5 minutes until frothy and pale in color.

Melt the unsalted butter and allow it to cool before adding to the egg mixture along with oil and vanilla extract. Mix until smooth.

Gently fold the sifted dry ingredients into the wet mixture using a rubber spatula, being careful not to overmix.

Fold in half of the roasted cherries and semi-sweet chocolate chips until evenly distributed.

Pour the brownie batter into the prepared pan and smooth the top. Bake for 40-50 minutes until edges set and center is slightly underdone.

Allow the brownies to cool in the pan for about 15 minutes. For easier cutting, freeze the pan for an additional 15 minutes. Remove and slice into squares.