INGREDIENTS:

For the chocolate crust:

• 1 1/3 cups ground chocolate wafers or chocolate graham crackers
• 1/3 cup peeled hazelnuts
• 3 tablespoons granulated sugar
• 6 tablespoons unsalted butter (3/4 stick), melted, plus more to coat the baking pan

For the filling:

• 3/4 cup granulated sugar
• 2 tablespoons all-purpose flour
• 1/4 teaspoon kosher salt
• 3 (8-ounce) packages cream cheese, at room temperature
• 3/4 cup chocolate-hazelnut spread, such as Nutella
• 1/4 cup heavy cream
• 2 teaspoons pure vanilla extract
• 3 large eggs plus 1 egg yolk, at room temperature

For the topping:

• 3/4 cup chocolate-hazelnut spread, such as Nutella
• 1/4 cup heavy cream
• 1/2 cup hazelnuts, toasted and chopped

INSTRUCTIONS:

1. Preheat the oven to 375°F and arrange a rack in the middle. Coat the bottom and sides of a 9-inch springform pan with butter.
2. In a food processor, process the crumbs and hazelnuts until they’re finely ground. In a bowl, stir together the crumb mixture, sugar, and melted butter until the crumbs are evenly moistened. Pour into the prepared pan and press evenly onto the bottom and about 1 1/2 inches up the sides. Bake until set, about 8 minutes. Let the crust cool on a wire rack. Reduce the oven temperature to 325°F.
3. To make the filling, mix together the sugar, flour, and salt in a bowl. In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese on medium speed until smooth. With the mixer running, pour in the sugar mixture and beat until incorporated. Stop the mixer occasionally to scrape down the sides of the bowl and the paddle as needed. Add the Nutella, cream, and vanilla and beat until well blended. Add the eggs and yolk 1 at a time, beating well after each addition. Scrape down the sides of the bowl and the paddle as needed.
4. Pour the filling into the crust and spread evenly. Bake until the filling is set and the center still jiggles slightly when gently shaken, about 1 hour. Turn off the oven and let the cake cool in the oven for 1 hour. Remove the cheesecake from the oven and let it cool on a rack for about 30 minutes.
5. To make the topping, in a saucepan over low heat, warm the Nutella and cream, stirring constantly, until smooth and completely combined. Let cool for about 5 minutes; the mixture should be smooth and spreadable. Pour over the top of the cheesecake, spreading it evenly. Let the cheesecake cool completely.
6. Cover and refrigerate the cheesecake until well chilled, at least 2 hours or preferably overnight. Remove the pan sides and run a long, thin knife between the pan bottom and the crust, then slide the cake onto a serving plate. Garnish with the chopped hazelnuts and serve.