Preheat your oven to 350°F and position a rack in the center. While the oven heats, prepare two 8½ x 4½ inch loaf pans by greasing them lightly with butter or cooking spray, then coat the insides generously with granulated sugar—this creates a delicate crust on the bread's exterior. Set the pans aside. Gather all your ingredients and ensure the eggs, cream cheese, and eggnog are at room temperature (this helps with proper emulsification and mixing). I like to use room temperature ingredients for quick breads because they incorporate more evenly and create a more tender crumb.

In a large mixing bowl, cream together the softened butter and both sugars (brown and granulated) using an electric mixer on medium speed for about 2-3 minutes until light and fluffy—this incorporates air and creates a tender crumb. Add the room temperature eggs one at a time, mixing well after each addition, then add the dark rum and mix until fully combined. The mixture should look smooth and creamy at this point.

In a separate bowl, sift together the all-purpose flour, baking powder, and baking soda to remove any lumps and distribute the leavening agents evenly. Add the salt, freshly grated nutmeg, and ground cinnamon to the flour mixture and whisk together until the spices are evenly distributed throughout. This dry mixture ensures your bread will have consistent rise and uniform spice flavor in every slice.

Add the dry ingredient mixture from Step 3 to the wet mixture from Step 2, starting with the chilled eggnog—alternate between adding a portion of the dry ingredients and a portion of the eggnog, beginning and ending with the dry ingredients. This technique prevents overmixing and ensures a tender crumb. Mix on low speed just until combined; the batter will be thick but pourable. Divide the batter evenly between the prepared pans, filling each about 3/4 full to allow room for rise.

Place both pans in the preheated 350°F oven and bake for approximately 45 minutes, or until a toothpick inserted into the center of each loaf comes out clean or with just a few moist crumbs. The tops should be golden brown. Allow the loaves to cool in the pans for 15 minutes, then carefully turn them out onto a wire rack to cool completely before frosting—this prevents the delicate crumb from getting soggy.

While the loaves cool, make the frosting by beating the room temperature cream cheese in a clean bowl with an electric mixer on medium speed for about 1-2 minutes until it becomes light and fluffy. Add the corn syrup, kosher salt, and vanilla extract, then whip on high speed for 30 seconds. Gradually add the sifted powdered sugar in 3-4 additions, mixing on low speed between additions and then whipping on high for a few seconds to incorporate air. I find that adding the sugar gradually prevents a gritty texture and creates a smoother frosting. Once all sugar is incorporated, add the eggnog one tablespoon at a time on low speed, tasting as you go, until you reach a spreadable consistency—you may not need all 8 tablespoons.

Once the cooled loaves from Step 5 are completely cool, spread or pipe the eggnog cream cheese frosting from Step 6 over the top of each loaf in an even layer. Finish with a light sprinkle of freshly grated nutmeg over the frosting for both visual appeal and extra spice flavor. Allow the frosting to set for a few minutes before slicing and serving.