Melt one-quarter cup of the butter in a nine-inch-square baking dish and sprinkle with the brown sugar. Arrange the pineapple slices and pecans in a design on top of the sugared butter.
Cream the remaining butter with the granulated sugar and beat in the egg and the vanilla. Stir in the sifted flour, baking powder and salt alternately with the milk.
Spoon the batter carefully over pineapple slices. Bake for about thirty-five minutes, or until done. Let cake stand for five minutes before inverting onto a serving platter. Serve warm with sour cream.