Combine zwieback crumbs, 2 tablespoons sugar and 2 tablespoons walnuts; blend in melted butter. Press mixture evenly on bottom and side of 8 inch springform pan. Chill.

Beat cream cheese with electric mixer at medium speed, in large bowl, until fluffy. Gradually beat in sugar and 1 teaspoon vanilla.

Beat in eggs, one at a time. Pour into a prepared pan. Bake at 350 degrees for 40 minutes or until center is firm. Remove from oven. Cool on wire rack 5 minutes, away from drafts.

Combine sour cream, remaining sugar and vanilla. Spread over top of cake, sprinkle with remaining walnuts if desired. Return to oven 5 minutes until topping is set. Remove from oven. Cool in pan on wire rack, away from drafts. Remove side of pan. Refrigerate several hours before serving.