Melt butter in a 9-inch cast iron skillet. Combine 1/2 cup brown sugar and 1 teaspoon cinnamon; sprinkle over butter in skillet. Arrange apple slices on sugar mixture. Set aside.
Combine shortening, 1/2 cup brown sugar, and molasses, creaming well. Add egg; beat well. Combine flour, soda, salt, and spices; add to creamed mixture alternately with buttermilk, beginning and ending with flour mixture.
Pour batter evenly over apple slices in prepared skillet. Bake at 350° for 50 minutes or until cake tests done. Cool 15 minutes, and invert onto plate. Serve warm with whipped cream, if desired.