In a bowl, combine wafers, nuts and butter. Press into a 9-inch springform pan. Bake at 325°F for 10 minutes. Let cool.
Combine cream cheese, Velveeta, sugar and flour, mixing at medium speed on mixer until blended well.
Add eggs, one at a time, mixing well after each addition.
Blend in sour cream, butter flavor and vanilla mixing until well blended.
Pour over cooled crust and bake at 450°F for 10 minutes.
Reduce oven temperature to 250°F and continue baking for 1 hour.
Loosen cake from rim of pan; cool before removing rim from pan.
Chill. Garnish with whipped cream, if desired.