Place butter and chocolate in a heatproof bowl set over a pot of simmering water.
4 tbsp unsalted butter
Stir until melted and smooth. Remove from heat.
In the clean bowl of a mixer fitted with the whisk attachment, add egg whites.
6 large eggs
Beat egg whites on medium speed with a hand or stand mixer until foamy, about 2 to 3 minutes.
In the large bowl add egg yolks and sugar.
1 cup white granulated sugar
Using hand or stand mixer with the whisk attachment, beat egg yolks and sugar on medium-high speed until pale, thick, and almost doubled in volume, about 4 minutes.
Add slightly cooled melted chocolate with butter in the egg yolk mixture.
Beat in chocolate mixture until just combined.
Beat in coffee mixture until just combined, scraping the sides.
Gently fold 1 cup egg-white mixture into chocolate mixture with a rubber spatula.
Fold in remaining egg-white mixture just until combined (do not overmix).
Pour into cooled crust until the top of the crust.
Bake until cake is cracked on top and set but still slightly wobbly in center, about 45 minutes. Let cool completely. Cake will deflate in center as it cools, and it is Ok. After it is cooled, cover and refrigerate overnight.
Chocolate Pudding
Whisk together sugar, cocoa, cornstarch, and salt in a medium saucepan.
1/2 cup unsweetened cocoa powder, 1/4 cup corn starch, 1/4 tsp kosher salt, 1/2 cup sugar
Whisk egg yolks and milk in the cocoa mixture.
4 large egg yolks, 2 cups whole milk
Bring a pot to a gentle boil over medium heat. Whisk constantly to prevent scorching.
Boil 30 seconds, then switch off the heat and add butter, and chocolate.
3 tbsp butter, 3.5 ounces dark chocolate
Whisk until melted and fully incorporated.
Set aside to cool, covered with a lid or plastic wrap, pressing it directly onto surface to prevent skin from forming.
Stir and spread pudding with a spatula on top of the cake.
Cover with plastic wrap and refrigerate until set, at least 3-4 hours.
Chocolate swirl decoration
Place chocolate in a heatproof bowl set over a pot of simmering water (Bain-Marie). Wait until it just melts.
5 ounces dark chocolate
Pour chocolate on the tray over the cold surface. Spread it in the thin layer, using an off set spatula.
When the chocolate is starting to set, place a knife under 30 angle and push away from you to make swirls.
Place swirls on a plate in a cool place until you are ready to decorate.
White Frosting
Place the cream with powdered sugar in a large whisking bowl (preferably cold).
2 tbsp powdered sugar, 2 cups heavy cream
Use a hand mixer or stand mixer with whisk attachment to beat until stiff peaks. You will need around 3-4 minutes, be cautious to not overdo this.
Unmold cake. Top pudding layer with whipped cream, spreading to edges. Place in the fridge before serving.
Leave the swirls on top.
Sprinkle Oreo crumbs and shave some chocolate.
Decorate with chocolate swirls.
Video
Notes
Start making the pie 1-2 days before.You can store the cake in the fridge for 3 days with whipped cream and 4 days without whipped cream. Store in the spring form pan, covered with plastic.