Preheat oven to 350 degrees. Grease a 13x9 inch baking pan.
Peel,core and chop the apples finely. Add 2 Teaspoons lemon juice to the apples, toss to combine. Set aside.
In a large mixing bowl beat the butter and white sugar until well incorporated.
Add the eggs and vanilla, beat until light and fluffy.
Sift the flour, baking soda, baking powder and salt together. Add to the egg mixture alternately with the sour cream. Beat mixture just until each addition of flour and sour cream are just incorporated into the batter. Stir in the chopped apples
Spread half the batter into the prepared pan. Sprinkle half the topping over the batter. Place the remaining batter over the topping, sprinkle with the remaining topping.
Bake at 350 degrees for 35 - 40 minutes or until toothpick inserted comes out clean. Remove from the oven, cool on a wire rack.
Place all topping ingredients into a medium bowl, rub the mixture between your fingers until butter is well distributed into the mixture.