Ingredients

• 1/4 pound wheatmeal crackers finely crushed (about 1 cup)
• 1 ounce fine-quality bittersweet chocolate (no more than 60% cacao if marked), grated
• 1/2 stick unsalted butter, melted
• 1/2 pound fine-quality bittersweet chocolate (no more than 60% cacao if marked), chopped
• 1 stick unsalted butter, cut into pieces
• 1 pound 2 ounce cream cheese, at room temperature
• 1/2 cup sour cream
• 1/4 teaspoon pure vanilla extract
• 2 large eggs
• 2/3 cup superfine granulated sugar
• 1 cup hazelnuts (4 1/2 ounces), toasted loose skins rubbed off in a kitchen towel while still warm, and nuts chopped
• Equipment: a 10-inch springform pan
• Accompaniment: lightly sweetened whipped cream

Instructions

1. Combine all ingredients, then press onto bottom of springform pan.
2. Make filling and bake cheesecake: Preheat oven to 325°F with rack in middle. Melt chocolate with butter, then remove from heat and whisk in cream cheese until smooth. Whisk in sour cream and vanilla. Whisk together eggs and sugar in a large bowl until mixture has a mousse-like consistency, then stir in chocolate mixture and nuts. Pour filling into crust and bake 1 1/2 hours. (Top will be slightly cracked.) Cool to room temperature in pan on a rack, about 1 hour, then chill at least 1 hour. (Cake will sink slightly.)
3. Preheat oven to 325°F with rack in middle.
4. Melt chocolate with butter, then remove from heat and whisk in cream cheese until smooth. Whisk in sour cream and vanilla.
5. Whisk together eggs and sugar in a large bowl until mixture has a mousse-like consistency, then stir in chocolate mixture and nuts.
6. Pour filling into crust and bake 1 1/2 hours. (Top will be slightly cracked.)
7. Cool to room temperature in pan on a rack, about 1 hour, then chill at least 1 hour. (Cake will sink slightly.)