1-First Step: Gather and prep Preheat oven to 350°F. Spray a 9-inch deep-dish pie pan with cooking spray. Make sure butter for the filling is at room temperature (about 67°F is ideal) and heavy cream is very cold (refrigerated). Chop the bittersweet baking chocolate and melt gently in a double boiler or short bursts in the microwave, stirring until smooth. Keep an instant-read thermometer handy for the egg step.

2-Second Step: Make the crust* Place 20 regular-stuffed chocolate sandwich cookies (230 grams) in a food processor. Pulse until finely ground.* Add 3 tablespoons unsalted butter, melted, and pulse until the crumbs are moistened and resemble wet sand.* Press the mixture firmly into the bottom and up the sides of the 9-inch deep-dish pie pan.* Bake at 350°F for 10 minutes until fragrant and set. Cool completely before filling.

3-Third Step: Cook eggs and sugar safely Whisk together 1 1/3 cups granulated sugar (266 grams) and 4 large eggs in a small saucepan. Cook over medium-low heat, whisking constantly until the mixture reaches 160°F and thickens enough to coat the back of a spoon, about 5 to 7 minutes. This temperature pasteurizes the eggs while keeping the mixture silky. Remove from heat and stir in 8 ounces bittersweet baking chocolate, melted (227 grams), and 2 teaspoons vanilla extract until smooth. Cool the mixture to about 75°F, stirring occasionally to keep it even. To speed cooling, transfer the chocolate-egg mixture to a stainless steel bowl with larger surface area.

4-Fourth Step: Whip the butter Beat 10 tablespoons unsalted butter, room temperature (142 grams), until light and fluffy, 2 to 3 minutes on medium speed. Gradually add the cooled chocolate-egg mixture and beat on high speed for 5 minutes until the mixture is lighter and airy. Proper whipping aerates the butter and gives the filling its signature silkiness.

5-Fifth Step: Fold in whipped cream Whip 1 1/3 cups cold heavy cream and 4 teaspoons powdered sugar to stiff peaks. Gently fold the whipped cream into the chocolate-butter mixture in three parts. Use a rubber spatula and fold with a light hand so the filling remains fluffy and mousse-like, not runny. Overmixing will deflate the air you just created.

6-Final Step: Chill, top, and serve* Pour the filling into the cooled crust, smoothing the top. The pie will be tall with filling; that is normal.* Refrigerate for at least 6 hours until fully set. For best slicing, chill overnight.* When ready to serve, whip 1 cup cold heavy cream with 2 tablespoons powdered sugar and 1 teaspoon vanilla extract to stiff peaks. Spread or pipe over the chilled pie and garnish with chocolate shavings or a dusting of cocoa powder just before serving.