• Line an 8-inch pan with plastic wrap, letting it overhang on all sides.

Make the bottom layer

• Place peanut butter and oil in the bowl of a stand-mixer and beat on medium-high speed until combined and light in color, 2 to 3 minutes. If you don't have a stand-mixer, just whisk it thoroughly.
• Reduce speed to low and add the melted milk chocolate until thoroughly combined.  Remove bowl from mixer and fold in the cornflakes.
• Pour into prepared pan and level with a spatula. Refrigerate until firm, about 30 minutes.

Make the top layer

• In a bowl of a stand mixer, whisk the cream until soft peaks form.  Place the melted semisweet chocolate in a medium size bowl and fold in half of the cream to lighten it and then quickly fold in the remaining half.  Pour the mixture over the bottom layer, making sure to reach the corners. Beat against the work surface to eliminate any air.  Cover with plastic wrap and refrigerate for at least 4 hours. (At this point the dessert can last 3 days).

Serve

• One hour before serving, lift the block from the pan using the overhang sides. Peel off the plastic and cut it into 4×1 inch bars with a large warm knife. Have a deep container of hot water nearby; dip the knife into the water, and dry with a kitchen towel before each cut. Eat! If feeling fancy, dust with cocoa powder, or serve with raspberries.