Preheat oven to 350F and grease one 9" X 5” loaf pan.
In a medium bowl, combine flour, baking powder, baking soda, salt, nutmeg, and cinnamon, whisk to combine.
Cream butter and sugars in stand mixer until pale & fluffy. Approx 3 minutes.
Add eggs one at a time, fully incorporating after each addition. Add rum and vanilla.
Alternate adding dry ingredients and eggnog making sure to fully incorporate into the batter between additions. Starting and ending with the dry (3 additions of dry, 2 of wet).
Pour into prepared pan and bake in center of oven until a toothpick comes out clean. Approx 40mins.
Cool in pan for 10mins, transfer to wire rack and cool completely before glazing.
For the glaze, combine all ingredients together until desired consistency.*
Notes
*For the glaze I just throw everything into a 4 cup measuring cup and mix it with a fork. Don't bother to sift the powdered sugar. Also, I kind of just wing it, so treat the amounts listed loosely. I usually just add more sugar or liquids until I get to the desired consistency.