Turn oven on to 350°F (175°C). Use heavy-duty foil or parchment paper to line a 9x9-inch baking pan, allowing overhang on at least two sides, then apply a light coating of nonstick cooking spray.

Stir together graham cracker crumbs, melted butter, sugar, and salt in a medium bowl until thoroughly mixed. Transfer this crumb mixture into the lined pan.

Firmly compact the crumbs into the pan's bottom with your hands or a spatula. Place in oven for 10 minutes.

Using a mixer on medium speed, whip the cream cheese in a large bowl until light and fluffy, roughly 2 minutes. Incorporate the granulated sugar and continue beating for another couple of minutes until velvety.

Add the eggs, egg yolk, eggnog, and vanilla; beat once more until fully blended and silky.

If using bourbon, incorporate it now and beat until evenly distributed; if not, proceed without. Lastly, beat in the flour, nutmeg, and salt until lump-free.

Transfer the eggnog cheesecake filling atop the graham cracker crust. For a water bath, set the baking pan inside a larger pan and pour in enough hot water to reach halfway up the sides of the baking pan.

Bake until barely set, 40 to 45 minutes. Take the baking pan out of the water bath and move it to a wire rack. Allow to cool for 30 minutes, then chill for at least 3 hours or overnight.

The cheesecake is ready when the center looks nearly set.

When baking the bars without a water bath, bake for about 30 to 40 minutes.

Take out of the oven and let cool on a baking rack for one hour. Refrigerate for at least 3 hours or overnight.

Lift from the pan using the foil, and slice into 16 bars. Dust with nutmeg, or with graham crumbs and/or crystallized ginger, or leave plain.