Heat oven to 450°F. Unroll pie crust; place in 10-inch tart pan with removable bottom. Press crust firmly against bottom and side of pan; trim edges. Bake 8 to 12 minutes or until light golden brown. Remove from oven to cooling rack. If crust puffs in center, flatten gently with back of wooden spoon. Cool 15 minutes.
Meanwhile, in 2-quart saucepan, heat 3/4 cup of the cream over medium heat until bubbles begin to form around sides of pan. DO NOT BOIL. Remove from heat. Stir in chocolate until melted. Stir in 1/4 cup of the mascarpone cheese and 6 tablespoons of the chocolate hazelnut spread until well blended.
In small bowl, beat egg yolks with fork. Gradually add about 1/4 of the melted chocolate mixture to the egg yolks, stirring constantly. Stir egg mixture back into the pan of hot chocolate cream. Cook over medium-low heat, stirring constantly for 3 to 5 minutes until mixture begins to thicken; remove from heat. Spread 1/2 cup of the chocolate mixture in bottom of cooled crust. Press 1 cup of the toasted hazelnuts into hot filling. Carefully spoon remaining chocolate filling over nuts. Refrigerate at least 1 hour or until completely cooled.
In medium bowl, beat remaining 1 1/4 cups cream with electric mixer on high speed until slightly thickened. Slowly add the remaining mascarpone cheese and the remaining 2 tablespoons chocolate hazelnut spread. Continue beating until stiff peaks form.
Pipe or spoon whipped cream mixture over top of cooled tart. Finely chop remaining 1/4 cup hazelnuts; sprinkle over whipped cream. Store covered in refrigerator.