Preheat the oven to 425°F.
Line a baking sheet with parchment paper. Set aside.
Add the flour, baking powder, sugar, cinnamon, and nutmeg to a large mixing bowl and whisk to combine.
Add the cold butter chunks to the mixing bowl and mix with your hands, or a pastry blender, ensuring the butter is thoroughly worked into the dry ingredients and the entire mixture is moistened.
Create a small well in the center of the dry ingredients/butter mixture and pour the eggnog into the well. Mix with a spoon to combine the ingredients, then use your hands, working from the bottom up and mxing until fully combined.
Turn the dough out onto the prepared baking sheet and form it into a thick disk shape.
Cut the dough disk carefully into 6 equal triangles using a sharp knife.
Bake the scones for 18 minutes until lightly golden brown.
Remove the scones from the oven and allow them to rest on the baking sheet for 5-10 minutes before separating them.
While the scones are resting, add the powdered sugar, milk, and rum extract to a small mixing bowl and mix until smooth.
Drizzle the glaze over the still-warm scones and top with a few sprinkles and extra cinnamon and nutmeg if desired.
Store any leftover scones in an airtight container for up to three days.