Preheat oven to 350℉. Lightly butter two 4½- inch springform cake pans and line bottom with parchment paper. Set aside.
Place chopped chocolate and butter in a microwave safe bowl. Microwave at half power (50%) for 20 second intervals until melted and mixture is smooth. Stir in between intervals to ensure even melting. Set aside and allow to cool slightly.
In a large bowl, combine egg yolks, Nutella, ground hazelnuts, and Frangelico. Mix until smooth. Add melted chocolate mixture and fold to combine.
In a medium bowl, add egg whites and salt. Using a hand mixer, beat egg whites to stiff peaks. Add ⅓ of egg whites to large bowl with chocolate mixture. Fold to combine. Add another ⅓ of egg whites and fold to combine. Repeat with remaining ⅓. Fold until there are no longer any egg white streaks.
Divide cake batter between the two prepared cake pans. Bake for 30-35 minutes until the cake has puffed up and the tops of the cake have cracks. Insert a toothpick in center of cake to test for doneness. Allow cakes to cool in pan for 5 minutes before unmolding. Allow to cool on wire racks.