- Vegetable oil for greasing pan
- 7 oz fine-quality bittersweet chocolate (not unsweetened), chopped
- 1 stick (1/2 cup) cold unsalted butter, cut into pieces
- 1/4 cup granulated sugar
- 1/4 teaspoon salt
- 3 large eggs, lightly beaten
- 1 teaspoon vanilla
- 1 cup salted dry-roasted peanuts (4 oz)
- 4 oz cream cheese, softened
- 1/2 cup creamy peanut butter (not “natural”)
- 3/4 cup confectioners sugar
- 1/4 teaspoon salt
- 1/2 cup chilled heavy cream
- 1 teaspoon vanilla
- 1/3 cup heavy cream
- 3 tablespoons light corn syrup
- 3 tablespoons packed brown sugar
- 2 tablespoons Dutch-process unsweetened cocoa powder
- 1/4 teaspoon salt
- 3 1/2 oz fine-quality bittersweet chocolate (not unsweetened), chopped
- 1/2 teaspoon vanilla
- Put oven rack in middle position and preheat oven to 350°F. Line a 9-inch square baking pan with foil, allowing 2 inches of foil to hang over 2 opposite ends of pan, and lightly brush foil (except overhang) with oil.
- Melt chocolate with butter, sugar, and salt in a double boiler or a large metal bowl set over a pan of barely simmering water, whisking occasionally, until smooth. Remove top of double boiler or bowl from heat and whisk in eggs and vanilla, then stir in peanuts.
- Pour batter into baking pan and bake until set and edges are slightly puffed, about 15 minutes. Transfer cake in pan to a rack to cool completely.
- Beat cream cheese, peanut butter, confectioners sugar, and salt in a bowl with an electric mixer at medium speed until combined well, about 4 minutes.
- Beat cream with vanilla in a bowl with cleaned beaters at medium-high speed until it just holds stiff peaks, then gently fold into peanut butter mixture until just combined.
- Spread mixture evenly on top of chocolate layer and freeze, pan covered with foil, until firm, about 2 hours.
- Bring cream, syrup, sugar, cocoa, salt, and chocolate to a boil in a 1-quart heavy saucepan over moderate heat, stirring until chocolate is melted. Reduce heat and simmer, stirring frequently, until thickened, about 3 minutes, then remove from heat. Stir in vanilla until incorporated. Cool sauce to warm.
- Carefully lift cake from pan by grasping overhang. Trim 1/4 inch from edges of cake and discard, then cut into 8 bars. Peel off foil and serve bars with sauce.