Preheat the oven to 350 degrees F, and grease 3 mini loaf pans or one standard-size loaf pan.
In a medium bowl, mix together the flour, baking powder, cinnamon, nutmeg, and optional dried cranberries. Set aside.
In a large mixing bowl, cream the butter and sugar. (A handheld or stand mixer may be used.) Add the eggs, beating after each addition. Then mix in the eggnog, rum and vanilla extract.
Add the dry mixture to the wet mixture, half at a time, mixing until the flour is just incorporated. Be careful not to over mix.
Transfer the batter to the prepared pan(s), and bake the mini loaves for 35-40 minutes and the standard size loaf for approximately 55-60 minutes. Check a few minutes early and add time as needed—cooking times will vary based on precise dimensions of pans and individual oven. (Helpful tip: The internal temperature when taken with a quick-read thermometer should read 200 degrees F.)
Cool 10 minutes, and then remove to a cooling rack. Cool completely before wrapping in plastic wrap or storing in a zip-top bag. May freeze.
If using the glaze, place the sugar in a small bowl and add the extract or rum. Stir in two tablespoons of the eggnog, and then add just enough additional eggnog to achieve a smooth, drizzling consistency. If you want more of an icing, keep the mixture on the thicker side. If you accidently add too much liquid, simply stir in a little more confectioner’s sugar. Drizzle the glaze over the cooled loaves and let dry before wrapping.