Preheat oven to 350°. In large mixing bowl combine first. flour, butter, and brown sugar. Blend together until crumbly, using a mixer on low speed. Stir in chopped pecans. Press 2 3/4 cups of crumb mixture into an ungreased 13X9-inch pan. To remaining mixture add cinnamon, soda, salt, sour cream, vanilla and egg. Blend well with mixer. Stir in chopped apples. Spoon evenly over crumb layer. Bake for 25 to 30 minutes, or until toothpick inserted in center comes out clean. Cut into squares and serve with whipped cream or ice cream, if desired. Serve warm or cold.