Melt 4 tablespoons butter in a 10-inch cast-iron skillet, sprinkle the brown sugar evenly over it and arrange the pineapple rings with one cherry in each center.
Whisk the flour, baking powder and salt together in a bowl.
Beat the remaining butter with the granulated sugar until fluffy, beat in the eggs and vanilla and alternate adding the flour mixture and milk.
Spread the batter carefully over the fruit without disturbing the pattern.
Bake at 350°F for 35 to 40 minutes until a tester in the cake portion comes out clean, cool for 10 minutes and invert onto a plate.