Melt 2 cups sugar in 2-quart heavy saucepan over medium heat, stirring constantly. Add cream, stirring briskly until well combined with sugar. Stir in nuts; cool, set aside.
Cream butter and 1/2 cup sugar until light and fluffy. Blend in eggs and vanilla extract. Add flour; mix well. Spread 2 cups dough onto bottom and 1 1/2 inches high around sides of 10-inch spring form pan. Spread nut mixture evenly over dough in pan. Roll remaining dough to 10-inch circle between wax paper. Place over nut mixture; pinch edges to seal. Brush with combined egg white and water. Bake at 350° F for one hour. Cool.
Dust with powdered sugar, if desired.Makes 16 Source: