Cream shortening and 1/2 cup butter; gradually add 2 cups sugar, beating until light and fluffy.
Add eggs, one at a time, beating well after each addition.
Combine 3 cups flour, baking powder, soda, and salt; add to creamed mixture alternately with buttermilk, beginning and ending with flour mixture.
Spoon half of batter into a greased and floured 13- x 9- x 2-inch baking pan.
Arrange apple slices over batter.
Spread remaining cake batter evenly over top.
Combine1/2.
cup flour, 1/2 cup sugar, and cinnamon, mixing well.
Cut in 3 tablespoons butter with a pastry blender until mixture resembles coarse meal; stir in chopped pecans.
Sprinkle mixture evenly over batter.
Bake at 350° for 45 minutes.
Cool completely.
Cut cake into squares to serve.