This is chocolate peanut butter pie turned into easy, sliceable bars! There's an Oreo cookie crust topped with rich smooth chocolate custard, creamy peanut butter mousse and lightly sweetened whipped cream with chocolate shavings. This is a cool treat everyone will enjoy!
Make the crust. Place the Oreos in a food processor and pulse until finely ground. Add melted butter and pulse until it is combined and looks damp. Tip it into the prepared 8x8-inch square baking pan and press it into the bottom in an even layer. Bake for 6-8 minutes at 350°F until just set and it feels dry. Let cool completely.
Make the chocolate custard layer. In a small 1-quart saucepan, combine sugar, corn starch and cocoa powder and whisk to blend evenly so there are no lumps of starch or cocoa. Very slowly begin to whisk in the cream so that it blends smoothly with the starch/sugar mixture. Once all the cream is added, you can pour in the milk and whisk well. Add egg yolks one a time and whisk them in evenly before each addition. Place the sauce pot over medium-low heat and whisk constantly until it starts to thicken. Be patient as this can take up to 10 minutes. Increase the heat slightly to medium if necessary, but do not walk away from the pan and do not stop stirring as it can easily catch and scorch at the bottom of the pan.
Once the mixture starts to thicken, lower the heat and watch carefully. Once it starts to bubble, let it bubble for just 5 seconds while stirring then immediately transfer it to a clean bowl. NOTE: you can pass it through a fine mesh sieve to remove any curdled egg pieces if you are so inclined.
Add the chopped dark chocolate and whisk until it is completely melted and evenly combined. Add butter and vanilla and stir it in until melted and evenly incorporated. Place a piece of plastic wrap directly over the surface of the custard to cover it and cool for 15 minutes in the fridge. Pour the chocolate custard over the cooled crust and spread it out evenly. Refrigerate for about 1 hour until set.
Make the peanut butter mousse. First whip the heavy cream in a medium bowl on medium-high speed until it forms soft peaks (3-5 minutes) and keep refrigerated. Place soft cream cheese in a large bowl and beat until smooth and creamy. Add sugar and beat until incorporated and mixture is glossy. Mix in peanut butter and vanilla on low speed. Scoop about ⅓ of the whipped cream into the peanut butter mixture and fold it in to loosen it up. Once it’s mostly combined, add in the rest of the whipped cream and continue to fold until it’s fully combined. Spread this evenly over the chocolate layer and chill again for about 30 minutes.
Make the topping. Whip the heavy cream and sugar in a medium bowl on medium-high speed until it forms soft peaks (3-5 minutes). Dollop it over the peanut butter layer, spread it out and make swooshes and swirls. Place the pan in the fridge for another hour to set.
Before serving, top with chocolate curls and chopped peanut butter cups. Serve chilled or at room temperature but store it in the fridge. Enjoy!
TIP: to make chocolate curls, place a large block of chocolate in the microwave for just 15 seconds or so to soften it, then use a vegetable peeler to shave down the long side of the block. Let the curls fall off naturally and make little curls.