Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper. Cut the fresh cherries in half and pit them. Spread cherries on the baking sheet, sprinkle with sugar, and bake for about 10 minutes. Cool while preparing brownie batter.
Lower your oven temperature to 325°F (160°C). Spray an 8x8 inch pan with non-stick spray and line the bottom with parchment paper.
Sift together flour, cocoa powder, cornstarch, and salt in a mixing bowl. Set aside.
In a mixer, beat together sugar, eggs, and egg yolk on high speed for about 5 minutes until thick and pale.
Melt the butter and let it cool slightly. Add to the mixer with oil and vanilla. Mix on low speed and fold in the dry ingredients with a rubber spatula.
Gently fold in half of the cooled roasted cherries and all of the chocolate chips.
Pour the batter into the pan and bake for 40-50 minutes until edges are set and center is slightly underdone.
After baking, sprinkle additional chocolate chips on top and let cool completely before removing from the pan. Top with remaining roasted cherries, cut into squares, and indulge.