01 -
Preheat oven to 350°F (175°C). Grease a 13×9-inch baking pan thoroughly.
02 -
In a large bowl, beat cake mix, vegetable oil, eggs, and sour cream until completely combined, about 2 minutes. Spread half of the batter evenly in the prepared pan.
03 -
In a small bowl, mix the brown sugar and cinnamon together. Sprinkle this mixture evenly over the batter in the pan. Carefully spread the remaining batter over the cinnamon-sugar layer and smooth the surface.
04 -
Bake for 45-50 minutes, or until the cake turns golden brown and a toothpick inserted in the center comes out clean.
05 -
While the cake is baking, make the glaze by combining melted butter, powdered sugar, milk, and vanilla in a small bowl. Stir until smooth and it reaches a thick, pourable consistency.
06 -
While the cake is still warm, use a fork or skewer to prick holes across the entire surface. Pour the glaze evenly over the cake, allowing it to seep into the holes. Let the cake cool completely before slicing and serving.