1. Stir together cookie crumbs, butter, sugar and salt in a medium bowl. Press into bottom and up side of a 9-inch pie pan (not deep dish). Refrigerate while preparing filling.Filling
2. Chop 21/2 of the chocolate bars. Combine eggs and 1/3 cup of the sugar in a large metal bowl or double boiler. Bring 2 inches of water to a simmer in a large pot or Dutch oven. Place bowl or double boiler over pan without touching water. Cook, beating constantly with a hand mixer, until mixture is light colored and fluffy, and registers 160 degrees on an instantread thermometer, 5 to 6 minutes. Watch carefully; if eggs get too hot, they will scramble.
3. Remove bowl from heat. Whisk in chopped chocolate and cocoa powder until smooth. Set aside to cool for 15 minutes, whisking occasionally.
4. Once egg mixture is cooled, combine remaining 1/3 cup sugar with the butter and salt in a large bowl. Beat on high speed until very light colored, about 2 minutes. On medium, beat in egg mixture, scraping down side of bowl. Fold in half of the whipped topping and spread into prepared crust. Refrigerate overnight.
5. Just before serving, spread center of pie with remaining whipped topping. Use a vegetable peeler to make large curls from reserved chocolate, or cut into shards and sprinkle over pie.