Preheat your oven to 350 degrees. Generously spray 2 jumbo muffin tins with non-stick cooking spray.
In a medium-sized bowl, mix the brown sugar and melted butter. Evenly divide sugar mixture into muffin tins. Add one pineapple slice and one maraschino cherry to each.
In a large bowl, whisk the flour, salt, and baking powder, set aside. In a separate bowl, mix together sugar and butter until light and fluffy. Mix in vanilla and eggs mixing in between each egg addition. Slowly alternate adding flour mixture and milk, mixing well between each. Divide the cake batter evenly between the tins.
Bake in the oven for 18-22 minutes until cake bottoms are golden and the cakes are cooked through. Once cooled, flip over the pans to remove your mini pineapple upside down cakes and serve.