Set aside 3/4 cup cake mix for topping. In a small bowl, combine gingersnap crumbs and remaining cake mix; stir in butter and egg. Press onto the bottom of a greased 13x9-in. baking dish; set aside., For filling, in a large bowl, beat cream cheese and brown sugar until smooth. Beat in eggs. Beat in the pumpkin, milk, cinnamon and vanilla and mix well. Pour over crust., For topping, in a small bowl, combine the gingersnap crumbs, sugar and reserved cake mix; cut in butter until crumbly. Stir in pecans. Sprinkle over filling. , Bake at 325° for 70-75 minutes or until filling is set and a thermometer inserted in the center reads 160°. Cool on a wire rack for 1-1/2 hours. If desired, garnish each serving with a gingersnap half. Store in the refrigerator.