1. Coarsely chop 1 tablespoon walnuts; reserve for garnish. In blender at medium speed or in food processor with knife blade attached, finely grind remaining walnuts.
2. Grease two 8-inch round cake pans; line bottoms of pans with waxed paper and grease paper. In medium-sized bowl, combine ground walnuts, flour, baking powder, and salt; mix well.
3. Preheat oven to 350°F. In large bowl, with mixer at high speed, beat egg whites until soft peaks form.
4. In small bowl, with same beaters and with mixer at high speed, beat egg yolks and sugar until very thick and lemon-colored. With rubber spatula or wire whisk, gently fold nut mixture, then yolk mixture into beaten egg whites just until blended.
5. Pour batter into prepared pans. Bake 25 to 30 minutes, until top of cake springs back when lightly touched with finger. Cool cake in pans on wire racks 5 minutes. Remove from pans; remove waxed paper and cool cake layers completely on wire racks.