Preheat the oven to 350.
Lightly grease a 10-inch cast iron skillet or a round cake pan (either will work fine)
Lay your pineapple rings in the bottom of your dish with the edges just touching. You should be able to fit 7 or so.
Add the cherries to the centers of each and sprinkle over the brown sugar; set aside.
In a large bowl, cream the butter and sugar with your hand or stand mixer until just pale and a little fluffy--about 2 to 3 minutes.
Add the eggs, one at a time and beat between each addition.
In a small bowl, mix the flour, baking powder and salt and stir to combine.
Add the flour in three batches, alternating with the buttermilk.
You should begin and end with flour. Don't overmix the batter.
Gently stir in the vanilla.
Pour the batter over the pineapple, coming within 1/4 of an inch of the top of your pan. You may have a little batter left over.
Bake for 40-45 minutes or until a toothpick inserted in the center comes out clean.
It's a good idea to bake yours on a cookie sheet or with a little foil under it in case it runs over.