Preheat oven to 350° with rack in center. Sift together onto a piece of parchment paper, 3/4 cup sugar, flour, cocoa powder, baking soda, and salt. Add grated chocolate; set aside.

In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites and cream of tartar until soft peaks form. With machine running, add remaining 3/4 cup sugar in a slow steady stream, beating until fully incorporated, and stiff glossy peaks form. Add vanilla and almond extracts; beat to combine.

Remove from mixer. Gradually add flour mixture, gently but thoroughly, folding into egg white mixture until fully combined. Pour into a 10-inch non-stick angel food cake pan. Tap pan on counter to remove any air bubbles. Bake until cake springs back when depressed with a finger, 30 to 35 minutes. Cool, inverted, 1 hour before removing pan. Serve with chocolate hazelnut anglaise.

Prepare an ice bath; set aside. In a medium bowl, whisk together 1/4 cup sugar and the egg yolks; set aside.

In a medium saucepan combine, remaining 1/4 cup sugar, heavy cream, milk, vanilla bean, and salt, over medium-high heat. Bring just to a simmer. Using a measuring cup or a ladle, slowly pour about 1/2 cup of the hot milk mixture into the egg-yolk mixture. Whisking constantly, keep adding milk mixture, about 1/2 cup at a time until it has all been added. Pour mixture back into saucepan

Cook over low heat, stirring constantly with a wooden spoon, until thick enough to coat back of a spoon, 1 to 5 minutes. Pour through a fine mesh sieve into a medium bowl, set over ice bath. Whisk in Nutella stirring occasionally until cool.

Cover, and transfer to refrigerator until completely chilled, at least 1 hour and up to overnight.