Fit the bottom of a 9-inch (23 cm) springform pan with a round of parchment paper, then butter the pan and dust with sugar and set aside. Melt the chocolate in a double boiler or gently in the microwave, 15 seconds at a time.
Fit an electric mixer with the whisk attachment, and beat the egg whites until they are foamy. Add the sugar, and beat until the whites form stiff peaks, about 2-3 minutes. In another bowl, use the mixer with the paddle attachment to beat the butter and chocolate-hazelnut spread together. Add the egg yolks, salt, and orange juice or cognac, and mix until fully incorporated. Then add in the melted chocolate, vanilla, and hazelnut meal, and mix until smooth.
Gently fold a quarter of the egg whites into the chocolate mixture to lighten it, and then add the rest of the egg whites and fold them in gently, being careful not to overmix. Pour the batter into the prepared pan and smooth the top. Bake until a tester comes out clean, about 40 to 45 minutes. Let the cake cool for about 10 minutes, then open the spring and remove the side ring, and slide the cake and parchment out of the pan and onto a serving plate. Allow the cake to fully cool before serving. Delicious topped with fresh whipped cream and orange zest.
Serve with whipped cream or fresh berries if desired.