Start by preparing your pie crust. If you're using a homemade flaky pie crust or a store-bought version, bake it completely according to the recipe or package directions, then allow it to cool fully before filling. If you're opting for a no-bake crust made from graham cracker or Oreo crumbs, simply prepare the crust and set it aside—no baking required.

(Pie crust, baked and cooled)

Finely chop the dark chocolate and place it in a large heatproof mixing bowl.

(10 oz dark chocolate)

In a small saucepan over medium heat, warm the heavy cream and vanilla extract until the cream is hot and steaming with tiny bubbles forming at the edges—do not let it come to a boil.

(1½ cups heavy cream, 1 teaspoon vanilla extract)

Pour the hot cream over the chopped chocolate and allow it to sit undisturbed for one minute. Then stir until the chocolate is fully melted and the mixture becomes smooth and glossy, forming a ganache. Transfer about one-third of the ganache (approximately ¾ cup) to a separate bowl and set it aside to use as the topping later. Keep both bowls at room temperature while you prepare the meringue.

Create a double boiler by adding 1 to 2 inches of water to a saucepan and bringing it to a gentle simmer over medium-low heat. In a heatproof bowl, combine the egg whites, granulated sugar, and salt, whisking them together. Place the bowl over the saucepan, making sure the bottom doesn't touch the simmering water. Whisk constantly until the mixture reaches 160°F (71°C) or until it's no longer grainy when rubbed between your fingers.

(4 large egg whites, 1 cup granulated sugar, ¼ teaspoon salt)

Transfer the heated mixture to a stand mixer fitted with the whisk attachment. Whip on high speed until glossy, stiff peaks form and the mixture has cooled completely—this usually takes around 10 minutes. If stiff peaks form but the bowl still feels warm, wait until it reaches room temperature before proceeding.

Now, fold the meringue gently into the larger portion of the ganache (not the reserved topping). The ganache should be completely cool—if it's still warm, chill it in the refrigerator briefly until it reaches room temperature, but be careful not to let it harden. Fold the meringue into the ganache in thirds, mixing gently after each addition until fully incorporated with no visible white streaks.

Pour the finished chocolate mousse into your prepared pie crust and spread it evenly. Refrigerate the pie for about 10 minutes to help it set slightly before adding the topping.

Once the mousse layer is slightly firm, pour the reserved ganache over the top and gently spread it to cover the entire surface. If the ganache has thickened too much to pour, gently warm it in the microwave in 5-second intervals until it's pourable but not hot.

Place the finished pie in the refrigerator to chill for at least 4 hours, or preferably overnight, to allow the layers to set completely. Serve chilled, and optionally top with a dollop of chantilly cream for an elegant finish.