As posted on Boston.com

Makes 16 squares

CRUST

• Butter (for the pan)
• Flour (for the pan)
• 1 2/3 cups chocolate wafer cookie crumbs
• 1/4 cup finely chopped peanuts
• 8 tablespoons (1 stick) unsalted butter, melted and cooled

1. Set the oven at 325 degrees. Butter a 9-inch square baking pan. Dust it with flour, tapping out the excess.
2. In a bowl combine the cookie crumbs and peanuts.
3. Pour the butter into the baking pan. Scatter the cookie crumb mixture in the pan in an even layer. Press down on the crumbs with a spatula. Bake the crust for 4 minutes. Transfer to a wire rack to cool.

BATTER

• 1 1/4 cups cake flour
• 3 tablespoons Dutch-processed cocoa
• 1/8 teaspoon baking powder
• 1/8 teaspoon salt
• 3/4 cup coarsely chopped peanuts
• 1 cup (2 sticks) unsalted butter, melted and cooled to tepid
• 4 ounces unsweetened chocolate, melted and cooled to tepid
• 3 tablespoons smooth peanut butter
• 4 eggs, lightly beaten
• 2 cups superfine sugar
• 2 teaspoons vanilla extract

1. In a bowl, sift the flour, cocoa, baking powder, and salt.
2. In another small bowl, toss the chopped peanuts with 1/2 teaspoon of the flour mixture.
3. In a large bowl, whisk the butter and chocolate. Stir in the peanut butter, blending it well. Add the eggs, sugar, and vanilla. Stir in the flour mixture, then the chopped peanuts.
4. Spoon the batter onto the crust, spreading it evenly, and taking care not to dislodge the layer of crust. Bake for 35 minutes or until just set. Transfer to a wire rack and leave to cool completely. Refrigerate for about 1 hour or until firm.
5. With a small sharp knife, divide the mixture into quarters. Cut each quarter into quarters again to make 16 squares. Use a metal spatula to lift the squares from the pan. Store in an airtight tin.