In a large bowl, whisk together flour and salt. Cut in the cold butter with a pastry blender or your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.

Gradually add ice water, 1 tablespoon at a time, mixing until the dough just comes together. Do not overmix.

Gather the dough into a ball, flatten into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Preheat oven to 400°F (200°C). On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Carefully transfer the dough to a 9-inch pie plate. Trim and crimp the edges as desired.

Line the pie crust with parchment paper and fill with pie weights or dried beans. Blind bake for 15 minutes. Remove weights and parchment paper and bake for another 5-7 minutes, or until golden brown. Let cool completely.

Melt the chopped bittersweet chocolate in a heatproof bowl set over a saucepan of simmering water (double boiler), stirring until smooth. Remove from heat and let cool slightly.

In a large bowl, beat the softened butter and granulated sugar until light and fluffy.

Beat in the egg yolks one at a time until well combined. Stir in the melted chocolate and vanilla extract.

In a separate bowl, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the chocolate mixture until just combined.

In a very clean bowl, beat the egg whites until stiff peaks form. Gently fold the beaten egg whites into the chocolate mixture until just combined. This step is crucial for the airy texture.

Pour the chocolate filling into the cooled pie crust and spread evenly. Cover the pie loosely with plastic wrap (do not let it touch the surface of the filling).

Refrigerate for at least 4 hours, or preferably overnight, until the filling is firm.

In a chilled bowl, whip the cold heavy cream with powdered sugar and vanilla extract until stiff peaks form.

Spoon or pipe the whipped cream over the chilled French Silk Pie. Garnish with chocolate shavings if desired.

Slice and serve immediately.