Preheat oven to 350°F . Lightly grease a 9-inch round cake pan and line the bottom with parchment paper for easy release.
In a large bowl, whisk the melted butter, granulated sugar, corn syrup, and brown sugar until smooth and combined. Add in the egg and vanilla extract and mix to combine.
½ cup unsalted butter, ¼ cup granulated sugar, ½ cup light brown sugar, 2 tablespoon light corn syrup, 1 large egg, 1 teaspoon vanilla extract
Stir in the flour, baking soda, cornstarch, and salt until just combined. Do not over-mix. Gently fold in the chocolate chips with a spatula.
1 & ¾ cup all-purpose flour, 1 & ½ tablespoon cornstarch, ½ teaspoon baking soda, ½ teaspoon salt, 1 & ½ cup semisweet chocolate chips
Spread the dough evenly into the prepared pan, making sure to push the dough all the way to the edges so it bakes level. For a super even surface, lightly press with an offset spatula or the bottom of a flat measuring cup.
Bake for 20–22 minutes, or until the top is lightly golden and the center is just set. Make sure that you don't over bake it, this is key for chewy texture.
Cool completely in pan before removing and slicing. This helps it firm up without crumbling.
Optional: Top with swirls of your favorite frosting ( I used a chocolate buttercream- see notes) and some sprinkles before serving!