Step 1

Preheat the oven to 350ºF. Spray a 9x13 inch pan with nonstick spray and set aside.

Step 2

In a mixing bowl, combine the cake mix, eggs, melted butter, and vanilla extract. Stir in the add-ins.The batter will be very thick.

Step 3

Transfer the batter to the pan and use a spatula or your hands to evenly distribute the batter across the pan. Top with additional add-ins if desired.

Step 4

Bake for 17-20 minutes or until the edges puff up and begin to set. Cool the bars completely before cutting.