Line an 8-inch square pan with plastic wrap, leaving an overhang.

Mince the lowfat milk chocolate coarsely.

In a metal bowl set over simmering water, heat the minced lowfat milk chocolate and whisk until smooth.

In another bowl, beat creamy peanut butter with Bailey's Irish Cream using an electric mixer until smooth.

Add the melted milk chocolate and crushed cookies to the peanut butter mixture and mix until well blended.

Pour the mixture into the prepared pan, smoothing the top with a spatula.

Cover with plastic wrap and refrigerate for about 2 hours, or until firm.

Mince the bittersweet chocolate coarsely.

In a metal bowl set over simmering water, heat the minced bittersweet chocolate and whisk until smooth.

Cool the melted bittersweet chocolate until tepid.

In a bowl with an electric mixer, whip heavy cream to soft peaks.

Gently fold half of the whipped cream into the melted bittersweet chocolate, then fold in the remaining whipped cream.

Pour the bittersweet chocolate mixture over the chilled lowfat milk chocolate layer.

Spread the bittersweet chocolate mixture evenly with a spatula, then tap the pan on the work surface to eliminate air bubbles.

Cover with plastic wrap and refrigerate for 4 to 6 hours, or until firm.

Remove the dessert from the refrigerator at least one hour before serving.

Lift the dessert out of the pan using the plastic wrap overhang.

Cut the dessert lengthwise into 1-inch strips using a knife dipped in warm water and dried.

Cut each strip in half crosswise to create two 4 x 1 inch bars.

Sieve cocoa powder over the top of the bars.

Place 2 bars on each of 8 plates, resting one edge of one bar on top of the second bar.

Let the bars sit at room temperature for about 1 hour before serving.