- 3/4 cup (1 1/2 sticks) unsalted butter, plus more for pan
- 12 oz good-quality bittersweet chocolate, coarsely chopped
- 6 large eggs
- 1 1/4 cups sugar
- 1 tsp salt
- 1 tsp vanilla extract
- 1 cup hazelnut spread, such as Nutella
- 1/4 cup milk
Preheat oven to 325°. Generously butter bottom and sides of a 9” spring form round pan. Line bottom of pan with parchment paper circle and butter.
To make the cake, in a bowl set over a saucepan of simmering water over medium-low heat, add butter and chocolate and let melt, stirring occasionally, about 8 minutes. Remove pan from heat and let cool to room temperature, stirring occasionally, about 10 minutes.
Meanwhile, in the bowl of a stand mixer fitted with the whisk attachment, add eggs, sugar, salt, and vanilla and beat on medium speed until pale yellow and fluffy and has a ribbonlike consistency, about 6 minutes.
Add in chocolate mixture and fold just until batter is combined. Do not overmix. Pour batter into prepared pan. Place on a baking sheet and bake until a thin, dry crust has formed on the surface, and cake barely wobbles at the center, 45-55 minutes. Transfer pan to a wire rack and let cake cool in pan about 15 minutes.
Place a large plate over pan. Using a towel to protect your hands, swiftly invert plate and pan, cake should release on its own. Lift pan off, then carefully peel off parchment. Let cool completely.
To make the glaze, in a small saucepan over medium-low heat, add hazelnut spread. Whisk milk into spread until thin and incorporated. Place in a pastry bag or resealable bag and drizzle over cake.