Preheat oven to 350°F.
Drain juice from canned pineapple into a measuring cup. Add water if needed to measure 1 cup. Set aside juice and 7 pineapple rings for the cake. Set any remaining juice and rings aside for another use.
20 ounces canned pineapple rings
Melt butter in a 10-inch cast iron skillet set over medium-high heat.
5 tablespoons unsalted butter
Remove the skillet from the heat and sprinkle brown sugar evenly over the top until all butter is covered.
1 cup brown sugar
Arrange 6 pineapple rings around the outer edge of the skillet and the remaining ring in the center without overlapping. Place a cherry in the center of each pineapple ring.
7 maraschino cherries
In a medium bowl, combine the flour, baking powder, and salt and set aside.
1½ cups all-purpose flour, 2 teaspoons baking powder, ¼ teaspoon kosher salt
In a separate medium bowl, combine brown sugar and softened butter. Using a hand mixer, beat for 2 minutes on medium speed until creamy.
⅔ cup brown sugar, ½ cup unsalted butter
Scrape down the bowl, then add the eggs one at a time, until well mixed. Stir in vanilla.
2 large eggs, 2 teaspoons pure vanilla extract
Gradually add flour mixture alternately with pineapple juice, beating at low speed and scraping the bowl often after each addition.
½ cup reserved pineapple juice
Pour the cake batter over the pineapple rings and spread it into an even layer.
Bake for 30-40 minutes, or until the middle is set and a toothpick inserted into the cake comes out clean.
Remove the cake from the oven and allow it to cool for 8-10 minutes, then run a knife or offset spatula around the edges to gently loosen the cake.
Set a plate over the skillet, then flip and carefully turn the warm cake out onto a plate. Transfer any fruit or glaze that sticks in the skillet back to the cake. Serve with whipped cream.