Preheat the oven to 325 degrees.
Melt the butter in a 10-inch heavy-bottomed skillet. Sprinkle the brown sugar uniformly over the bottom. Peel, core, and cut apples into one-half inch crosswise slices. Arrange them in the bottom of the skillet, overlapping the edges.
Combine the next 7 ingredients in a mixing bowl and mix well. Beat in the egg. Stir in the molasses. Add the milk alternately with the flour. Beat in the hot water.
Spoon the batter over the apples and bake for 45 to 50 minutes or until a toothpick inserted in the center comes out clean. Cool in the pan 10 minutes, then invert onto a serving plate, but do not remove the pan for 5 minutes. This permits sugar and butter topping to run down over cake. Serve with the whipped cream, if desired.
Makes one 9-inch square gingerbread.