Prepare Cream Filling. Cover and chill as directed.
Allow egg yolks and egg whites to stand at room temperature for 30 minutes. Meanwhile, line two 8×1 1/2-inch round baking pans with waxed paper; grease and flour pans.
Preheat oven to 350 degrees F. In a medium bowl stir together the graham crackers, flour, baking powder, and salt; set aside. In a large mixing bowl beat the shortening with an electric mixer on medium to high speed about 30 seconds. Add sugar and vanilla; beat until well combined. Add egg yolks; beat until combined. Alternately add the flour mixture and the milk, beating on low to medium speed after each addition just until combined. Stir in nuts.
Thoroughly wash the beaters. Beat the egg whites with an electric mixer on high speed until stiff peaks form (tips stand straight). Gently fold egg whites into the batter. Spread batter into the prepared pans. Bake for 20 to 25 minutes or until a toothpick inserted near the center comes out clean. Cool on wire racks for 10 minutes. Remove from pans. Cool cakes completely on the racks.
Place a cake layer, bottom side up, on a serving plate. Spread chilled Cream Filling on top of cake to within 1/4 inch of edge. Top with second cake layer, bottom side down. Spread sides and top with Brown Sugar 7-Minute Frosting. Cover; chill until serving time. If desired, top with additional graham crackers. Makes 12 servings.
In a medium saucepan combine sugar, flour, and salt. Stir in milk. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Remove from heat. Gradually stir about 1/2 cup of the hot milk mixture into egg yolks. Pour milk and egg mixture into saucepan. Bring mixture to a gentle boil. Reduce heat. Cook and stir for 2 minutes more. Remove from heat. Stir in vanilla. Pour into a bowl; cover with plastic wrap. Chill thoroughly.
In the top of a double boiler combine brown sugar, water, egg white, and cream of tartar or corn syrup. Beat with an electric mixer on low speed for 30 seconds. Place over boiling water (upper pan should not touch water). Cook, beating constantly with the electric mixer on high speed, about 7 minutes or until frosting forms stiff peaks (tips stand straight) and an instant-read thermometer inserted in the mixture registers 160 degrees F. Remove from heat; add vanilla. Beat 2 to 3 minutes more or until frosting is of spreading consistency.