Pour the melted butter into a 9-inch cake pan or cast-iron skillet.
Evenly sprinkle the light brown sugar over the melted butter, then arrange the pineapple rings on top and place Maraschino cherries in the centers of the rings and in any open spaces.
Preheat the oven to 350°F.
In a medium bowl, whisk together the all-purpose flour, baking powder, and Kosher salt; set aside.
In a large mixing bowl using a stand mixer or hand mixer, cream the sugar with the softened unsalted butter on medium until slightly fluffy and pale in color, about 3 to 4 minutes, scraping down the sides of the bowl as needed.
Whisk in the eggs, pineapple juice, and vanilla extract until combined.
With the mixer running on low, add half of the flour mixture, mix until incorporated, then add half of the milk. Repeat with the remaining flour and milk and mix until fully combined; the batter will be somewhat thick.
Use a spatula to transfer the batter into the prepared pan and gently spread it evenly over the pineapple rings and cherries.
Bake until a toothpick inserted into the center comes out clean, about 45 minutes.
Let the cake rest for 10 minutes, then carefully invert the cake onto a cake stand or serving plate.
Slice and serve warm or at room temperature; optionally serve with ice cream or whipped cream.