Preheat oven to 350 degrees F (180 degrees C) and grease an 8-inch square baking pan and line with parchment paper, leaving a 2-inch overhang on all sides.
Whisk together Corn Starch (1/3 cup), Unsweetened Cocoa Powder (1/4 cup), Ground Cinnamon (1 teaspoon) and Salt (1/2 teaspoon) in a smaller mixing bowl and set aside.
In a large bowl, microwave Unsalted Butter (6 tablespoon) and Semi-Sweet Chocolate Chips (12 ounce) in 30-second increments, stirring each time, until melted and smooth, about 2 minutes.
Stir in Granulated Sugar (3/4 cup) and Pure Vanilla Extract (1 1/2 teaspoon) to butter and chocolate mixture then stir in Large Egg (3), one at a time, until combined.
Add cornstarch mixture to wet ingredients and stir until mixture is smooth and begins to pull away from side of bowl, about 2 minutes.
Pour batter into pan and smooth top. Bake until a toothpick inserted in center comes out with a few moist crumbs attached, about 35 minutes, rotating pan halfway through.
Let cool completely in pan on a wire rack. Using paper overhang, lift cake out of pan and cut into 16 squares. Serve and enjoy!