Chocolate Peanut Crunch Bar Cake

Make the milk chocolate layer: Line an 8-inch square baking pan with
plastic wrap, leaving a 2-inch overhang

on two sides. Melt the milk chocolate according to the melting
instructions in the Chocolate Key. In a medium bowl, using a
hand-held electric mixer, beat the peanut butter and oil on medium
speed until smooth. Beat in the cookie crumbs and chocolate. Scrape
the chocolate mixture into the prepared pan. Spread with a rubber
spatula in an even layer. Tap the pan on the counter to remove any
air bubbles. Cover the pan with plastic wrap and freeze 20 minutes or
until firm. Make the bittersweet chocolate layer:

Melt the dark chocolate according to the melting instructions in the
Chocolate Key. Transfer the chocolate to a large bowl. Stir in the
oil. In a chilled large bowl, using a hand-held electric mixer, beat
the cream on high speed just until soft mounds begin to form. (Do not
overwhip the cream. ) Using a rubber spatula, quickly fold 1/2 of the
whipped cream into the chocolate mixture to lighten it. Fold in the
remaining cream. Scrape the bittersweet chocolate mixture over the
milk chocolate layer. Spread in an even layer. Tap the pan on the
counter to remove any air bubbles. Cover the pan with plastic wrap
and refrigerate at least 6 to 8 hours. (The cake may be prepared 2
days in advance. ) Unmold the cake: Using the plastic wrap as
handles, lift the cake from the pan. Slide the cake off the plastic
wrap onto a cutting board. Dust the top of the cake with cocoa
powder, if desired. Using a long sharp knife dipped in hot water and
wiped dry, cut the cake into 1-inch strips. Cut each strip in half to
make eight 4-by-1-inch bars. Allow the bars to stand at room
temperature before serving. Arrange 2 bars on each dessert plate.