Chocolate Peanut Crunch Bar Cake

For the milk chocolate layer, line an 8-inch square pan with plastic
wrap, leaving an overhang. Melt milk chocolate in the top of a double
boiler above gently simmering water and whisk until smooth. Beat the
peanut butter and oil using an electric mixer until smooth. Mix in
the milk chocolate and cookies until well blended. Pour into the
prepared pan, smoothing the top with a spatula. Bang the pan on a
work surface to even contents. Cover with plastic wrap and
refrigerate until firm, for about 2 hours. For the bittersweet
chocolate layer, melt the bittersweet chocolate in the top of a
double boiler above gently simmering water and whisk until smooth.
Cool to tepid. Meanwhile, whip cream to soft peaks. Quickly fold 1/2
of whipped cream into the chocolate, then fold in the remainder. Pour
over the firm, chilled milk chocolate layer. Spread with spatula
until smooth. Bang on a work surface to eliminate air bubbles. Cover
with plastic wrap and refrigerate until firm, for about 4 to 6 hours.
(This can be prepared several days ahead.) To serve, remove from the
refrigerator at least 1 hour before serving. Immediately lift the
chocolate dessert out of the pan. Cut lengthwise into 1-inch wide
strips using a knife rinsed in hot water and dried, then cut each
strip in half crosswise to form two 4- by 1-inch bars. Sieve cocoa
powder over the tops of the bars. Place 2 bars on 8 plates, resting 1
edge of 1 bar dramatically atop the second bar. Let sit at room
temperature about 1 hour before serving. This recipe yields 8
servings.