Wash hands with soap and water.
Heat oven to 350 °F. Line 13×9-inch baking pan with aluminum foil, extending over edges. Set aside.
Combine flour, graham cracker crumbs, baking powder, baking soda and salt in bowl. Set aside
Beat butter, sugar and brown sugar in large bowl until creamy. Add egg, egg yolk and vanilla; beat until well combined. Slowly add flour mixture; beat until just combined. Spread batter into prepared pan.
Wash hands with soap and water after handling eggs and flour.
Bake 26 to 30 minutes. Remove pan from oven and lay chocolate bars over cookie. Return to oven for 2 minutes. Using an off-set spatula spread the melted chocolate over the graham cookie layer. Let cool completely until chocolate is set.
For the frosting, place about 1/2inch water into bottom pan of double boiler. Bring to boil over high heat. Combine 3/4 cup sugar,1/4 cup water, egg white, corn syrup, cream of tartar and salt in top of double boiler.
Wash hands with soap and water after handling eggs.
Place mixture over rapidly boiling water (water should not touch bottom of pan); beat at highest speed with hand mixer 7 minutes or until mixture forms stiff peaks. (Do not overcook.) Remove from heat; add vanilla. Continue beating 2 minutes or until frosting holds deep swirls.
Lift bars from pan using foil ends. Remove foil. Frost top of bars. Use kitchen torch to toast frosting. Let sit 5 to 10 minutes before cutting to allow frosting to set.