Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round pan that is at least 2 inches deep and line the bottom with parchment paper. Alternatively, you can use an 8×8 square baking dish.
In a small bowl, mix together the sugar and cornstarch. Toss the pitted cherries with this mixture. If using frozen cherries, allow them to thaw for about 20 minutes before proceeding.
Evenly spread the cherries across the bottom of the prepared pan.
In a large mixing bowl, combine all the ingredients for the chocolate cake batter. Use an electric mixer to beat for 2 minutes until smooth.
Slowly pour the cake batter over the cherries, ensuring an even layer.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 5 minutes before carefully turning it out onto a heat-proof serving plate.