Heat the oven to 350° F.

In a small bowl, melt the butter. You can use the microwave on low.

Set a round 9" cake pan or a 9"x9" square baking dish on a baking sheet. Spray cake pan with cooking spray.

Pour the melted butter into the cake pan.

Sprinkle the brown sugar over the butter evenly.

Arrange the pineapple slices on top of the brown sugar in a pattern that fits them without overlapping. You can cut the remaining slices in half to fit into the gaps (see photo).

Place a maraschino cherry in the center of each pineapple ring, and in the gaps as you like.

In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt.

In a 2-cup glass measuring cup, whisk together the buttermilk, sour cream, egg, oil, rum extract, and the vanilla.

Pour the wet ingredients into the dry ingredients and fold to combine. Don't overmix!

Pour the batter evenly over the pineapple in the baking dish.

Bake for 35-40 minutes, or until the cake is light golden brown and a toothpick inserted in the center comes out clean.

Set the cake pan on a wire rack to cool for a minimum of 30 minutes before inverting onto a serving plate.

Slice and serve.