Preheat oven to 350º.
Sift flour, baking powder and salt together and set aside.
Place a 8X8X2 cast iron skillet or cake pan in oven with 3 Tbsp. butter until butter is melted.
Remove skillet and add brown sugar, ensuring that entire surface is covered.
Arrange pineapple slices in pan.
Cream sugar and butter in a mixing bowl. Add egg and vanilla mixing well. Alternately add flour mixture and pineapple syrup to the sugar mixture, mixing well between each addition.
Spread mix in pan.
Bake 1 hour at 350.
Cool 10 minutes then invert cake on serving dish.