Preheat oven to 350°F and spray a pie plate with cooking spray.

Place Oreos in a food processor and process until fine crumbs form. Combine crumbs and butter in a medium-sized bowl and stir until crumbs are evenly coated.

Press crust into the prepared pie plate. Bake 18 minutes and remove from oven. Let cool completely.

(I did this step the night before. Once the crust has cooled, cover with plastic wrap or aluminum foil.)

Place chocolate and coconut oil in a heat-safe dish and microwave in 30 second intervals, stirring between each, until melted and smooth.

Place peanut butter in a heat-safe dish and microwave for 15 seconds, or until runny. Stir into melted chocolate.

Place egg whites, sugar, and cream of tartar in a heat-safe bowl (I used my metal stand mixer bowl). Boil two inches of water in a medium saucepan and set the bowl on top. Make sure the bottom of the bowl does not touch the boiling water. Whisk egg white mixture continuously until sugar has dissolved, about 4 minutes. Remove from heat.

Whip egg white mixture on high speed with an electric mixer (I used my stand mixer with the whisk attachment) until glossy and stiff peaks form.

Fold meringue into the melted chocolate/peanut butter. (The mixture will be thick and your arm might get tired from stirring!)

Clean stand mixer bowl and whisk attachment. (Or use a new bowl and clean electric mixer beaters.) Add heavy whipping cream to bowl and mix on high speed until stiff peaks form. Fold whipped cream into the meringue mixture.

Add half of mousse filling to the prepared pie crust. Spread with a rubber spatula. Sprinkle with half of Reese's cups and crushed Oreos. Drizzle with chocolate syrup.

Top with remaining filling and spread over Reese's cups and Oreos.

Warm peanut butter in a heat-safe dish in the microwave for 15 seconds.

Beat heavy whipping cream on high speed with an electric mixer or in the bowl of a stand mixer with the whisk attachment.

With mixer running, add vanilla, powdered sugar, and peanut butter. Mix until stiff peaks form.

Spread whipped cream on top of pie and sprinkle with remaining Reese's cups and Oreos. Drizzle with chocolate syrup.

Chill pie in the refrigerator for at least 1 hour. Cut into slices to serve. Store covered in the refrigerator.