Preheat oven to 350 degrees. Grease a large 12''x17'' jelly-roll pan (or similar size); set aside. For the Cookie Base: Combine flour, soda, salt and cornstarch; set aside. In a large mixing bowl, cream together softened butter, sugar and brown sugar. Mix in the vanilla and then the eggs, one at a time. Add the dry ingredients and mix until just incorporated. Stir in the chocolate chips. Press cookie dough evenly into prepared pan. You might not think there is enough dough to fill the entire pan, but there is. Bake in preheated oven for 17 minutes. Do not over bake. Remove from oven and cool completely.

For the Cheesecake Layer: Combine cream cheese and sour cream and mix, using a hand mixer, until combined. Add the powdered sugar and vanilla and mix together until smooth and creamy. Fold in the Cool Whip. Spread over cooled cookie bars. Top with chopped strawberries. Keep refrigerated until ready to serve (remove from fridge 15 minutes before serving). Slice and serve.