Place A Rack In The Center Of The Oven, And Preheat The Oven To 275°F.
Lightly Butter And Flour An 8″ Square Baking Pan.
Shake Out The Excess Flour, And Set The Pan Aside.
Place The Graham Cracker Squares In A Plastic Bag And Crush With A Rolling Pin, Or Place In Batches In A Food Processor Fitted With A Steel Blade And Pulse Until Finely Crushed.
Set Aside 1 Cup Crushed Graham Cracker Crumbs.
Place The Egg Yolks In A Medium-Size Bowl, And Beat With An Electric Mixer On Medium Speed Until Thick And Lemon Colored, 2 To 3 Minutes.
Gradually Beat In The Sugar Until Thickened.
Blend In The Vanilla And Set Aside.
In A Small Bowl, Stir Together The Graham Cracker Crumbs, Salt, Walnuts, And Baking Powder.
Fold This Mixture Into The Egg Yolk Mixture And Set Aside.
With Clean Beaters, Beat The Egg Whites Until Stiff Peaks Form, 3 To 4 Minutes.
Fold The Egg Whites Into The Batter Until Just Combined.
Turn The Batter Into The Prepared Pan.
Tent The Pan With Aluminum Foil, And Place The Pan In The Oven.
Bake The Cake For 20 Minutes, Then Remove The Foil And Bake Until Golden Brown And Cooked Through, 45 To 50 Minutes More.
