Preheat oven to 350. Prepare a 9" springform pan with cooking spray and flour; set aside. To prepare crust, combine cake mix, margarine, and 1/4 cup walnuts. Mix until well blended. Press into bottom of prepared pan. Bake for twenty minutes. Remove from oven. Increase oven temperature to 450. To prepare filling, combine cream cheese, brown sugar, flour, egg whites, vanilla extract, and remaining walnuts. Pour filling mixture into crust. Bake for seven minutes. Reduce oven temperature to 250. Bake for 35 minutes or until set. Cool completely. Refrigerate two hours or until ready to serve. Brush top with maple syrup.