Pour melted butter into the bottom of an 8 inch square pan. Tilt the pan so that it is evenly coated. Sprinkle the brown sugar over the butter. Arrange the apple slices to cover the brown sugar, set aside. In a medium bowl, cream together the shortening and white sugar. Beat in the egg and vanilla until light and fluffy. Combine the flour, baking powder, and salt, stir into the creamed mixture alternately with the milk. Pour into the baking pan so that the fruit is completely covered.
Bake for 40 to 50 minutes in the preheated oven, until a toothpick inserted, comes out clean. Immediately invert onto a serving plate. Serve warm with ice cream or sauce.