Prep the pan and heat the oven.
Set your oven to 350°F. Generously coat your loaf pan (or mini pans) with baking spray so the bread comes out easily after baking.

Combine the dry components.
In a medium mixing bowl, whisk together the flour, instant vanilla pudding mix, baking powder, salt, and nutmeg until evenly blended and a bit aerated. This quick whisk helps the raising agent distribute evenly.

Cream the butter and sugar, then add the wet aromatics.
In a large bowl, beat the softened butter with the granulated sugar until the mixture becomes pale and fluffy (about 2–3 minutes). Add the eggs one at a time, beating well after each addition so the batter becomes smooth and cohesive. Stir in the vanilla, rum, and orange zest, then fold in the cold eggnog until just combined.

Fold the dry into the wet.
Add the dry mixture to the wet mixture and gently fold with a spatula until the batter is uniform and you no longer see streaks of flour. Work carefully—overmixing will make the crumb dense and tough.

Transfer batter and bake.
Spoon the batter into your prepared pan and level the surface. Bake mini loaves for roughly 30 minutes; bake a full-size loaf for about 45–55 minutes. The bread is done when the top is golden and a skewer or toothpick inserted into the center comes out clean or with a few moist crumbs.

Whisk the rum glaze while the loaf bakes.
While the bread is in the oven, make the glaze by whisking together the sifted powdered sugar, eggnog, rum, and nutmeg until smooth and pourable. Aim for a thick but drippy consistency—add a touch more eggnog if it’s too stiff.

Cool briefly, then glaze.
Allow the loaf to rest in the pan for about 10 minutes, then invert onto a cooling rack. Once it has reached room temperature, pour the rum glaze over the top and let it run down the sides. Give the glaze 15–20 minutes to set before slicing.