Preheat the oven to 350°F (175°C).

In a bowl, combine graham cracker crumbs, melted butter, and sugar. Mix until well combined.

Press the crumb mixture into the bottom and sides of a 9-inch pie pan.

Bake for 8-10 minutes until set. Let it cool completely.

In a heatproof bowl, melt the chopped semisweet chocolate over a pot of simmering water, stirring until smooth. Remove from heat and let it cool slightly.

In a separate bowl, whip 1 cup of heavy cream until soft peaks form. Set aside.

In another bowl, beat the egg yolks with 0.5 cups of sugar and vanilla extract until pale and thick.

Fold the melted chocolate into the egg yolk mixture until well combined.

Gently fold in the whipped cream until no streaks remain.

In a clean bowl, beat the egg whites until stiff peaks form, then fold into the chocolate mixture.

Pour the mousse filling into the cooled crust, smoothing the top with a spatula.

Refrigerate for at least 2 hours or until set.

Whip the remaining 1 cup of heavy cream until soft peaks form.

Spread the whipped cream over the set mousse pie, and garnish with chocolate shavings.

Slice the pie into wedges and serve chilled.