In a small bowl, combine the wafer crumbs, butter and brown sugar. Press onto the bottom of a greased 13-in. x 9-in. baking dish. Bake at 350° for 5-8 minutes or until lightly browned. Cool.
In a microwave-safe bowl, melt vanilla chips; stir until smooth. Cool. In a large mixing bowl, beat cream cheese and sour cream until smooth. Add melted chips; beat well. Fold in whipped topping.
Pour over crust. Cover and refrigerate for 2 hours or until set. Drizzle with chocolate topping if desired. Yield: 15 servings.