Mix until crumbly. Pat into 9 x 13 inch pan, greased. Prepare 1 package lemon pudding as per directions on package. Reserve these egg whites also. Cool lemon pudding 10 minutes. Spread over crust. Beat the 4 reserved egg whites until foamy. Add 1/2 cup sugar, 1/4 teaspoon cream of tartar and 1/2 teaspoon vanilla. Beat until stiff peaks form. Spread over lemon pudding. Bake at 350 degrees for 30 to 35 minutes. Cool completely. Cut into squares.