Preheat oven to 425 degrees F. Mix 1/2 cup of the milk, sour cream and 3 Tbsp. sugar in large bowl with wire whisk. Stir in baking mix until just blended. Spread evenly into greased 9-inch round cake pan. Bake 12 to 15 min. or until top is golden brown. Remove from pan; cool completely on wire rack.
Meanwhile, combine dry pudding mix and remaining 1/2 cup milk; blend well. Gently stir in half of the whipped topping until well blended. Mix strawberries and 1/3 cup sugar in large bowl; set aside. Slice cake in half horizontally to make 2 layers.
Place bottom cake layer on serving plate; top evenly with half of the strawberry mixture. Spread with pudding mixture; top with top cake layer. Spread with remaining whipped topping; top with remaining strawberry mixture. Serve immediately. Store leftover shortcake in refrigerator.