Preheat the oven to 350°F. Spray a 9x13 (or 13x9) baking dish with baker’s spray. (Baker’s Joy or generic version)

Add the cake mix, sour cream, vegetable oil, and eggs to a medium-sized mixing bowl (2 to 3-quart size). Using a handheld mixer, beat the ingredients together on medium-low speed until the cake batter is smooth.

Add half of the cake batter to the prepared baking dish. Using an offset spatula or a large spoon, smooth the cake batter over the bottom of the pan. (The batter will appear not to be enough to make 2 layers of cake, but it will expand as it bakes)

Add the brown sugar and ground cinnamon to a small mixing bowl. Stir to combine.

Sprinkle all of the cinnamon and sugar mixture over the bottom cake batter layer.

Spoon the cake batter over the cinnamon mixture layer. Carefully use either an offset spatula or a silicone spatula to smooth the top layer of cake batter over the cinnamon mixture layer. Bake for 28-32 minutes, depending on your oven, or until the top is golden brown and a toothpick inserted comes away clean. Make the glaze as soon as the cake comes out of the oven.

Add the sifted powdered sugar to a medium-sized mixing bowl (2 to 3 quarts). Whisk in the half and half and vanilla. Whisk until no lumps remain, and the glaze is smooth. Evenly spread the glaze over the top of the cake. (This works best when the cake is still hot) Allow the cake to cool for 1 hour before cutting 3 slices x 4 slices. You can eat this while it’s still a bit warm, or you can cool the cake completely.