• Preheat your oven to 350°F. Grease a 10-inch cast iron skillet, 9-inch round cake pan or 9-inch springform pan and set it aside.

Prepare the pineapple layer.

• Remove the pineapple slices from the can and blot them as dry as possible with paper towels. Reserve the juice from the can for the cake batter.
• Remove the cherries from the jar, remove any stems and blot them dry as well.
• Place the brown sugar and salt in a medium-size bowl and mix to combine. Add the melted butter, and mix until a thick, grainy paste forms.
• Transfer the brown sugar and butter mixture to the prepared baking pan, and spread into an even layer with a spoon or small offset spatula.
• Place one pineapple ring in the very center of the pan, on top of the brown sugar mixture. Arrange as many more of the pineapple rings in a single layer around the center ring as possible without overlapping them at all.
• Slice the remaining pineapple rings into quarters and arrange the pieces in gaps between the rings and along the edges of the pan, climbing up the sides.
• Place a maraschino cherry in the center of each whole pineapple ring. Set the pan aside.

Make the cake batter.

• In a large bowl, place the flour, xanthan gum, milk powder, baking powder, baking soda, salt, and sugar, and whisk to combine well.
• Create a well in the center of the dry ingredients and add the butter, eggs and pineapple juice, mixing to combine after each addition. The batter should be thick but smooth.
• Scrape the batter into the baking pan on top of the pineapple layer and spread into an even layer with a wet spatula, taking care not to disturb the pineapples or cherries. If using a springform pan, wrap the bottom tightly with heavy-duty aluminum foil as it will leak during baking.

Bake the cake.

• Place the pan in the center of the preheated oven and bake until a toothpick inserted in the center of the cake (but without reaching all the way to the pineapple layer on the bottom) comes out with a few moist crumbs attached (about 45 minutes, less for a cast iron skillet).
• Remove the cake from the oven and allow to cool in the baking pan until cool to the touch (at least 30 minutes).
• Invert the cooled cake onto a serving platter, removing the pan (or springform pan bottom) slowly so as not to disturb the pineapple layer. The cake should come out of the pan readily.
• Allow to cool completely before slicing and serving.