Preheat oven to 350°F and spray an 8 or 10-inch cast iron skillet with cooking spray. (You can also use a 9-inch round cake pan -- see note)
On the stovetop, melt butter on medium heat.
Sprinkle brown sugar evenly over butter in pan. Add cherry halves evenly to brown sugar layer, cut side down.
Spoon crushed pineapple over cherries and pat with the back of a spoon to distribute evenly. Set aside.
In a large bowl or stand mixer, beat sugar, eggs, & vanilla for one minute.
Stir in oil, buttermilk, and juice and mix well.
Add flour, baking powder, and salt and mix with a spoon until just combined.
Pour into pan and bake for about 30-35 minutes or until a toothpick inserted into the center of the cake comes out clean.
Allow to cool in the pan for at least 10 minutes, then carefully invert onto a cake plate. If any of the pineapple sticks to the pan, just scrape it off and gently add to the top of the cake.
Notes
I used a Lodge 10.25" skillet for this recipe, which was a good size -- the cake, when baked, rose to the edge of the skillet. You can also use an 8- or 9-inch cake pan, although I haven't tested that option. Let me know your results if you try the cake that way!