Preheat the oven to 350 degrees F. Grease a 9 by 13-inch pan
Using an electric mixer cream the butter, sugar, and brown sugar; then add the eggs and mix in.
Sift together the dry ingredients and gradually add to the creamed mixture alternating with the buttermilk. Add 1/3 of the flour mixture first and then 1/2 of the buttermilk and repeat.
Fold in the sliced apples and spread into the prepared pan.
Prepare the topping. Mix the brown sugar, granulated sugar, cinnamon, and pecans together. Sprinkle over the top of the cake.
Place the cake in the preheated oven and bake for 35 to 40 minutes. Remove from the oven and cool completely.