Preheat the oven to 350°F. Spray a 9-inch deep pie dish with cooking spray or brush lightly with melted butter.

Make the crust. Place Oreo cookies in the bowl of a food processor and pulse until finely ground. Add in the melted butter and pulse until moistened. Press the mixture evenly into the bottom and up the sides of the prepared pie dish. Bake for 10-15 minutes, or until fragrant and set. Transfer to a wire rack and let cool completely.

Make the filling. First combine chopped chocolate and butter in a heatproof bowl and set it over a saucepan with 1-inch of simmering water. Stir until melted and smooth. You can melt it in the microwave while stopping to stir after every 20 seconds. Set it aside to cool.

Bring a small pot filled with 1 inch of water to a simmer over medium heat. In a heat-proof bowl, combine eggs with half of the sugar (½ cup or 100g) and whisk to blend well. Place the bowl over the pot so it rests on top and make sure the bottom doesn’t touch the water. Whisk constantly while over the heat until the mixture reaches 165 degrees F on a digital thermometer.

Remove the bowl from over the heat and place it on a tea towel. Beat the egg mixture on high speed while gradually adding the remaining ½ cup of sugar, and continue to beat until very pale, thick and tripled in volume (ribbon stage). This will take 3-5 minutes. Mix in espresso powder if you're using it. Add the cooled chocolate mixture and vanilla extract, then gently whisk until it in. Let it cool for about 30 minutes while stirring occasionally until the mixture doesn’t feel warm but isn’t solidified.

Pour cream into a clean bowl and start beating on medium speed until it thickens, then increase speed and beat until it forms soft peaks. Fold the whipped cream gently into the whipped chocolate mixture in 2 or 3 stages until no white streaks remain. Pour this luscious mixture into the cooled crust. Place it in the fridge and let it set for at least 4 hours or up to 24 hours.

Make the topping. Pour cream into a clean bowl and beat on medium speed until thickened. Then, sift in the powdered sugar and beat until soft peaks form. Spoon the whipped cream on top of the chilled pie and top with dark chocolate curls.