Melt the butter and divide between two 8" cake pans.
Sprinkle the brown sugar evenly to cover the butter (divided as well).
Next, arrange pineapple rings around the bottom of the pans, one layer deep (I had 5 rings per pan). Place a maraschino cherry into the center of each pineapple ring (and a few in the middle if you would like).
In a large mixing bowl, mix the white rice flour, tapioca starch, salt, baking soda, baking powder and xanthan gum together and set aside.
Mix the eggs, sugar and mayonnaise until fluffy. Add the flour mixture, milk and vanilla and mix well.
Pour the batter over the pineapple layer (dividing the batter between the two pans).
Bake for 25-30 minutes at 350 degrees F. Cool for 5 minutes, then carefully turn out onto a plate. Do not let the cake cool too much, or it will be stuck to the pan.
Recipe by The Baking Beauties at http://www.thebakingbeauties.com/2009/04/gluten-free-pineapple-upside-down-cake.html