Prepare and Bake the Crust

1. Add both flours, brown sugar, salt, and all the spices to a food processor. Give it a few pulses to mix.
2. Drop in the cold butter and pulse several times until the mixture looks like coarse crumbs.
3. In a small bowl, whisk one of the eggs with the molasses. While the processor is running, pour this mixture in and keep processing until the dough comes together in a soft ball.
4. Remove the dough, shape into a disk, and wrap in plastic. Chill for about an hour, or until firmer but still pliable. (If you want to make little cookies for decorating, trim off a couple ounces of dough now and refrigerate separately.)
5. Lightly flour your work surface, roll the dough into an 11-inch circle, and ease it into a 9-inch pie plate. Crimp as desired and place the whole thing in the freezer for about 15 minutes.
6. Heat the oven to 375°F. Position one rack near the bottom and one in the center.
7. Line the chilled crust with parchment and fill with pie weights (rice or beans also work). Bake on the lower rack for 20 minutes. Remove the weights and parchment, then bake another 5–10 minutes until the crust looks set and lightly golden.
8. While the crust is still warm, separate the remaining egg. Lightly whisk the white and brush it all over the hot pie shell. The residual heat should cook it; if not, pop it back in the oven briefly until the coating looks dry. Set aside.
9. Reduce the oven temperature to 325°F.

Make the Custard

1. In a medium bowl, whisk the sugar, nutmeg, salt, and eggs together.
2. Add the eggnog, vanilla, and bourbon (if using). Whisk until smooth.
3. Pour the mixture through a fine strainer twice for the silkiest texture.
4. Carefully fill the baked crust with the custard. Use foil or a pie shield around the edges so they don’t darken too much.
5. Bake on the middle rack for 50–60 minutes. The edges should puff slightly, while the center should still jiggle just a little when nudged. Target temperature: around 180°F.
6. Cool the pie on a rack, then chill for at least 6 hours to let the custard fully set.
7. Add whipped cream, a sprinkle of nutmeg, or those gingerbread-cookie cutouts when serving.