Preheat oven to 350° F. Grease a 12-inch cast iron skillet and set aside.
Cut the drained cherries in half. Pat dry with a paper towel. Transfer to a small bowl and toss with cornstarch to coat.
In a large bowl, combine melted butter, and sugars. Stir until smooth. Add the egg, egg yolk, and vanilla and mix until combined.
Add the flour, cornstarch, baking soda, and salt. Mix until flour is incorporated (be careful not to overmix). Gently fold in chocolate chips and cherries.
Spread batter evenly in prepared cast iron skillet. Bake for 20-22 minutes or until golden brown. (Don't over bake, you want the cookie to be slightly gooey.)
While the skillet cookie is baking, make the cherry sauce. In a small saucepan, combine the reserved cherry juices with the cornstarch and sugar. Bring to a boil, and then reduce to a simmer. Simmer for a few minutes, until the sauce thickens and coats the back of a spoon. Remove from heat and allow to cool. (The sauce will thicken as it cools, you can always re-heat and add a little water to thin it out, if needed.)
Remove from the oven and let cool for 15-30 minutes. Serve warm with ice cream and cherry sauce, if desired.