01 -
Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish or line it with parchment paper. In a large bowl, combine the yellow cake mix, melted butter, eggs, and vanilla extract. Mix until smooth and well-combined. Spread the batter evenly into the prepared baking dish.
02 -
In a small bowl, mix together the cinnamon and brown sugar. Sprinkle the mixture evenly over the cake batter. Use a knife or toothpick to gently swirl the cinnamon-sugar mixture into the batter. Avoid overmixing to maintain a distinct swirl pattern.
03 -
Place the baking dish in the preheated oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the bars cool in the baking dish for about 10 minutes, then transfer them to a wire rack to cool completely.
04 -
In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth and creamy. Adjust the consistency with additional milk if necessary. Drizzle the glaze over the cooled bars.