In a large bowl combine the gingersnap crumbs and melted butter. Press into the bottoms and sides of a 9-inch pie plate. Bake pie crust for 10 minutes. Let cool completely.

In a medium saucepan warm the eggnog over medium heat until it starts to steam, but do not let it boil. Meanwhile in a large bowl whisk together the egg, egg yolks, cornstarch and sugar. Add the warm eggnog to the egg mixture in a small steady stream while whisking constantly until completely combined.

Return the mixture to the saucepan and place over medium heat. Cook until thickened, whisking almost constantly, about 5 minutes. Once thick, reduce heat to low and cook for 2 minutes more. Remove from heat and whisk in vanilla and bourbon, if using.

Cool eggnog mixture completely, either in the fridge for several hours or over an iced water bath.

In the bowl of a stand mixer fitted with a whisk attachment, or in a large bowl with a hand-held mixer, beat the whipping cream to soft peaks. Gently fold it into the eggnog mixture. Pour the filling into the gingersnap crust and chill for at least 2 hours. For firmer slices, chill for at least 4 hours.

To make the topping, beat the whipping cream to soft peaks. Stir in sugar and vanilla extract. Spread on top of pie and dust with freshly grated nutmeg.

Store pie in the fridge for up to 3 days.