Melt 1/4 cup butter in a 10-inch cast-iron skillet over medium-high heat; add 1 cup sugar, and cook, stirring often, 2 minutes or until sugar is melted and begins to turn golden. Add apple slices, and cook, stirring often, 5 minutes or until apples have softened slightly and juices are thickened and syrupy. Remove skillet from heat, and sprinkle apple mixture with 1/2 cup pecans. Set aside.
Beat remaining 1/2 cup butter at medium speed with an electric mixer until creamy. Gradually add remaining 1 cup sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
Stir together flour, baking powder, and cinnamon; add to butter mixture alternately with milk, beating at low speed just until blended, beginning and ending with flour mixture. Stir in remaining 1/2 cup pecans. Spoon batter evenly over apple mixture in skillet.
Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool in skillet 5 minutes; invert onto serving plate.