Heat oven to 350 degrees F. Coat 15 x 10 x 1-inch jelly-roll pan with nonstick cooking spray. Line bottom with parchment paper or waxed paper. Coat with spray.
Process 1-1/3 cups sugar, hazelnuts, 3/4 cup almonds and cornstarch in food processor until finely ground.
Beat whites, cream of tartar, and salt in bowl until soft peaks form, 2 minutes. Sprinkle ground nut mixture over whites; gently fold in. Pour into prepared pan, quickly spreading. Bake in 350 degree F oven 20 to 25 minutes, until pale golden brown. Remove pan to rack and let cool.
Coat small baking sheet with nonstick cooking spray. Sprinkle 1/2 cup sugar in even layer into heavy-bottomed, medium-size saucepan (do not use nonstick). Melt over medium-high heat until sugar turns light amber and caramelizes, 10 minutes. Remove from heat. Using wooden spoon, stir in 1/2 cup almonds. Pour mixture onto prepared sheet, quickly spreading in even layer. Let cool. When praline is cooled, break into pieces; place in food processor or in heavy-duty plastic bag. Process or crush plastic bag with rolling pin until praline is finely crushed.
Heat 3/4 cup creme fraiche in small saucepan over medium-low heat just until tiny bubbles begin to form around edge of pan. Remove from heat. Stir in chocolate until melted and smooth. Let stand until thickened and cooled.
Beat 3/4 cup creme fraiche, heavy cream, 2 tablespoons sugar and vanilla in medium-size bowl until consistency of butter. Combine 2/3 cup of the creme fraiche mixture and the finely crushed praline in small bowl.
To remaining creme fraiche mixture, add Cognac, whisking together until stiff peaks form.
Using serrated knife, gently slice around edges of meringue to loosen from pan. Place waxed paper-lined large cutting board on top of meringue; invert pan and board. Remove pan. If meringue sticks, gently pry one corner loose. Carefully peel off parchment or waxed paper. (If meringue breaks, don't worry; just patch together when assembling layers.) With serrated knife, trim crusty edges. Cut meringue lengthwise into four 10 x 3-1/2-inch rectangles.
Cover baking sheet with plastic wrap. Place one meringue rectangle in center of plastic wrap. Spread meringue with 3/4 cup ganache. Cover and refrigerate remaining ganache. Top with second rectangle; spread with Cognac-flavored cream. Layer on third rectangle; spread with praline cream. Top with remaining meringue rectangle. Wrap Marjolaine completely in plastic wrap; refrigerate overnight.
. To serve, heat remaining ganache in top of double boiler over hot water, or in small bowl in microwave oven 1 minute, until smooth and spreadable. Spread over sides and top of cake. Refrigerate 30 minutes for ganache to set. Slice crosswise with thin serrated knife, wiping blade between cuts. Serve with whipped cream. Marjolaine will keep in refrigerator for several days. Makes 16 servings.