PREHEAT oven to 350°F. Beat egg yolks, margarine and sugar in large bowl with electric mixer on medium-high speed until well blended. Combine graham crumbs, baking powder and salt. Add to egg mixture alternately with the milk, beating until well blended after each addition. Blend in vanilla.
BEAT egg whites in small bowl with electric mixer on high speed until stiff peaks form. Add to graham mixture; stir gently until well blended. Pour evenly into 2 greased 8-inch round cake pans.
BAKE 20 min. or until toothpick inserted in centers comes out clean. Cool 10 min. Remove from pans to wire racks; cool completely.
PLACE 1 of the cake layers on serving plate; spread top of cake layer with half of the whipped cream. Sprinkle with half of the walnuts; cover with remaining cake layer. Spread top with remaining whipped cream; sprinkle with remaining walnuts. Store in refrigerator.