Make cake batter. In a large bowl, or large bowl on stand mixer, bring together softened butter, brown sugar, sour cream, milk, egg, vanilla extract, and pineapple juice. Whisk to combine. Add flour, baking powder, baking soda, and salt to the mixture. Fold to combine.
Make topping. Pat dry pineapple rings and maraschino cherries, and set aside. Heat cast iron skillet and add butter. Once butter melts, switch off heat, and sprinkle brown sugar onto melted butter. Immediately add pineapple slices and maraschino cherries.
Pour cake batter onto pineapple rings and cherries. Use a spatula to evenly spread out cake batter.
Bake at 350℉ for 40 minutes.
Remove pineapple upside down cake from oven. Let it cool for 20-30 minutes.
Place a large plate onto cast iron skillet, then gently flip cake over with plate in the bottom.
Serve and enjoy!
Notes
In a pinch, plain yogurt can be used instead of sour cream
Use milk with 1% or higher fat content. The higher the fat content the softer and creamier cake will be.
When making the topping, don't completely melt the brown sugar in butter. Simply sprinkle it on there and top immediately with pineapple rings and cherries.
It is important to pat dry pineapple rings and cherries with paper towel before placing it on skillet so that your topping will not be watery.
Let skillet pineapple upside down cake cool for 20-30 minutes before flipping it upside down. I typically don't have issues removing cake from the cast iron skillet due to a buttery topping and the non-stick quality of cast iron skillets.