Preheat your oven to 350°F (175°C). Prepare a baking pan by greasing it lightly for easy removal of the bars.
In a small bowl, mix together the melted butter and light brown sugar. Spread this mixture evenly on the bottom of the prepared pan.
Arrange the pineapple slices over the sugar mixture and place a maraschino cherry in the center of each pineapple slice.
In a large bowl, combine the yellow cake mix, granulated sugar, and baking powder.
Add the pineapple juice, milk, vegetable oil, and vanilla extract to the dry ingredients. Mix until smooth.
Pour the cake batter evenly over the pineapple and cherry layer.
Bake in the preheated oven for 30 minutes. Then, cover the pan with aluminum foil and bake for an additional 15 minutes, or until a toothpick inserted into the center comes out clean.
Let the bars cool completely before enjoying.