Preheat oven to 350 F. In a small bowl, combine brown sugar and melted butter. Evenly divide the brown sugar mixture between two 12 cup muffin pans. Place one pineapple slice in each muffin cup along with one cherry.
In a large bowl, whisk together flour, granulated sugar, brown sugar, salt, and baking powder. Add in eggs, melted butter, pineapple juice, and vanilla extract. Whisk until smooth.
Evenly divide the mixture over the pineapple and cherries. Bake for 25-30 minutes. Turn each cake up side down onto a wire rack. Let cool completely.