Preheat oven to 350°. Line bottom of a greased 9-in. springform pan with parchment; grease paper.
In a microwave, melt chocolate chips and butter; stir until smooth. Cool slightly. In a large bowl, beat eggs, sugar and salt. Stir in vanilla and chocolate mixture. Add flour, mixing well. Stir in 1 cup hazelnuts.
Spread into prepared pan. Bake 55-60 minutes or until a toothpick inserted in center comes out with moist crumbs (do not overbake). Cool completely in pan on a wire rack.
Meanwhile, use plastic wrap to line a 4-qt. bowl with a 9-in.-diameter top. Quickly spread ice cream into bowl. Freeze, covered, until firm.
Loosen sides of brownie with a knife; remove rim from pan. Transfer brownie to a serving plate and remove paper. Spread top with Nutella. Invert ice cream mold onto brownie; remove bowl and plastic wrap. Immediately press remaining hazelnuts onto ice cream. Freeze, covered, at least 1 hour before serving. Cut into wedges.
Editor’s note: To toast whole hazelnuts, spread hazelnuts in a 15x10x1-in. baking pan. Bake in a 350° oven 7-10 minutes or until fragrant and lightly browned, stirring occasionally. To remove skins, wrap hazelnuts in a tea towel; rub with towel to loosen skins.