Chocolate Hazelnut Meringue Cake

For Chocolate Cake:

Preheat oven to 350ºF / 180ºC. Butter a 9-x-3-inch / 23 x 8 cm springform pan. Line bottom with parchment paper. Butter parchment and set aside.

In the bowl of an electric mixer fitted with the paddle attachment, whip the butter and brown sugar at medium speed until pale and smooth, about 3 minutes. Add egg yolks, one at a time, beating well after each addition and scraping the bottom and sides of your bowl as necessary. Add the melted chocolate, vanilla, rum, and salt. Beat until combined. Transfer mixture to a clean bowl and wash your mixing bowl thoroughly.

In the clean mixer bowl fitted with the whisk attachment, beat the 6 egg whites on high speed until soft peaks form, about 2 minutes. Fold one-third of the egg whites into chocolate mixture. Fold in remaining egg whites and pour batter into prepared pan, and bake 25 minutes.

For Meringue Topping:

Combine the chopped chocolate, nuts and cornstarch in a small bowl, and set aside. Place egg whites in a clean mixer bowl fitted with the whisk attachment, beat on high speed until frothy. With the mixer running, slowly add the sugar and continue beating until stiff peaks form, about 8 minutes. Fold in chocolate and hazelnut mixture.

To Assemble: Remove cake from oven. Using a large offset spatula, spread meringue mixture on top of cake using as few strokes as possible so the meringue does not deflate. Return cake to oven. Bake until meringue is lightly browned and crisp, 25 to 30 minutes.