Melt the butter in a 9-inch cast iron skillet. Add the brown sugar and pecans; stir well to thoroughly combine, then turn off the heat -- don't cook it. Arrange 8 pineapple slices in a single layer over the brown sugar mixture (your 9-inch skillet should accommodate 8 slices without overlapping). Set the skillet aside.
Combine the flour, baking powder and salt in a bowl; set aside.
Beat the egg yolks at medium speed until they are thick and lemon colored. Gradually add the sugar, continuing to beat. Add the flour mixture to the yolk mixture, and stir in the reserved pineapple juice.
Beat the egg whites until stiff peaks form. Fold the whites into the cake batter. Pour or spoon the batter evenly over the pineapple slices.
Bake at 350°F for 40 to 45 minutes. Cool the cake in the skillet for 30 minutes; then invert it onto a serving plate. Place a maraschino cherry in the center of each pineapple ring.