Preheat your oven to 325 degrees.

By hand, blend the cake mix, eggs, sour cream, and oil until well-incorporated. The mixture will be pale yellow; it’s okay if it has some lumps! Then set aside.

In a separate bowl, mix together the brown sugar and cinnamon until well-blended; set aside.

Pour half of the cake batter into a greased 13×9 pan, spreading the batter out into a thin layer. Add half of the swirl mixture to the top, covering the entire layer of batter. Don’t be alarmed if it looks like you’re over-saturating the cake—it’ll taste great! Pour the rest of the batter on top, and spread the batter until the cake is even. Top the cake off with the rest of the swirl mixture. With a knife, swirl the batter until you create a beautiful masterpiece (I always pretend I’m a barista pouring cream into a cappuccino because I’m really nerdy like that).

Place the cake into the oven and bake for 45-50 minutes, or until an inserted toothpick comes out clean.

While the cake is baking, make the glaze. In a bowl, mix the powdered sugar, milk, and vanilla until glaze is of desired consistency. When the cake comes out of the oven, immediately pour glaze onto the hot cake. You might have to pick up the cake and tilt it to spread the glaze evenly. Let the cake sit for a few minutes so the glaze can set and serve warm or at room temperature.