Preheat oven to 325°F. Line the bottom and sides of a 13x9-inch baking pan with parchment paper, extending paper over opposite sides of pan; lightly coat with nonstick cooking spray.

In a medium bowl stir together cookie crumbs and ¼ tsp. kosher salt. Stir in melted butter until well combined. Firmly press crumb mixture into bottom of the prepared pan. Bake until set, 10 minutes. Let cool in pan on a wire rack while making filling.

For custard, place egg yolks in a medium heatproof bowl. In a large saucepan whisk together sugar, cornstarch, and ½ tsp. kosher salt. Whisk in milk until smooth. Cook over medium-high, stirring constantly, until bubbly, about 6 minutes. Reduce heat to medium-low; cook, stirring constantly, 2 minutes more. Remove from heat.

Gradually add half of the hot milk mixture to egg yolks while whisking yolks constantly. Return egg yolk mixture to the remaining milk mixture in saucepan. Cook, stirring constantly, over medium until thickened, about 2 minutes. Remove from heat. Whisk in peanut butter and vanilla until smooth. Spoon onto crust; spread evenly. Cover with plastic wrap touching the surface. Chill 1 ½ hours.

For ganache, place chocolate in a medium heatproof bowl. In a small saucepan heat cream over medium until gently simmering. Pour over chocolate; do not stir. Let stand 5 minutes. Gently stir until chocolate is melted and ganache is smooth.

Pour ganache over custard layer and spread evenly. Chill, uncovered, until firm, at least 1 ½ hours or up to 12 hours.

Loosen bars from edges of the pan with a thin spatula. Using the parchment paper, lift uncut bars from pan and place on a cutting board. Cut into 20 bars. Top with Chocolate Whipped Cream and, if you like, garnish with cocoa powder and peanuts.

For Chocolate Whipped Cream, in a large bowl combine heavy cream, powdered sugar, and unsweetened cocoa powder. Beat with a mixer on medium just until soft peaks form.