Step 1

Preheat oven to 350°F (177°C). In a food processor or blender, pulse 22 Oreos (including the cream filling) into a fine crumb. You should have about 2 cups (packed) crumbs, or 250g. Pour crumbs into a large bowl. Add the melted butter and stir to combine. The mixture will be thick and quite wet. Try to smash/break up any large chunks. Pour the mixture into an ungreased 9-inch pie dish. With medium pressure using your hand, pat the crumbs down into the bottom and up the sides to make a compact, thick crust. Bake for 10 minutes, and then cool completely.

Step 2

Microwave the chopped chocolate and butter together in a large heat-proof bowl, stopping and stirring every 20 seconds until completely melted. Set aside.

Step 3

Place egg whites, sugar, and cream of tartar in a heatproof bowl. Set bowl over a saucepan filled with 2 inches of simmering water. Do not let the bowl touch the water. (You can use a double boiler if you have one.) Whisk constantly until sugar is dissolved, about 4 minutes. Whisking constantly, cook the egg mixture until the sugar is dissolved and the mixture reaches 160°F (71°C) on an instant-read thermometer. Transfer the mixture to the mixing bowl of your stand mixer fitted with a whisk attachment. Beat on high speed for 5–6 minutes until soft, glossy peaks form. See photo above for a visual. Gently fold mixture into the chocolate. Wash the mixer bowl and whisk attachment clean.

Step 4

Using a handheld or stand mixer fitted with a whisk attachment, beat the 2 cups of heavy cream on high speed until stiff peaks form, about 4-5 minutes. Gently fold whipped cream into the chocolate/egg white mixture. Do not overmix; it will deflate the mousse. (No need to wash or wipe the bowl/whisk attachment clean—you’ll make sweetened whipped cream in step 6.)

Step 5

Spread 1/2 of the mousse into cooled pie crust. Top with Oreo crumbs. (The 6 whole Oreos crushed into crumbs!) Top with remaining chocolate mousse, mounding in the center to create a dome shape. Place in the refrigerator for 5 minutes as you prepare the whipped cream topping.

Step 6

Using a handheld or stand mixer fitted with a whisk attachment, beat the 1 cup of heavy cream, granulated sugar, and vanilla on high speed until slightly stiff peaks form, about 4 minutes. You want the peaks to be somewhat soft so the whipped cream spreads nicely on the mousse. Remove pie from the refrigerator and spread whipped cream on top—once again keeping that dome shape in the center.

Step 7

Top with chocolate shavings, if using. Refrigerate pie uncovered for at least 4–5 hours or overnight. Slice and serve. Usually the 1st slice isn’t as beautiful as the 2nd! It’s easier to cut after you have 1 slice out.