Place a rack in the centre of the oven and preheat the oven to 350°F (175°C) or, if the pan has a dark finish, 325°F (160°C).
Butter a large 10 cup Bundt pan with softened butter (make sure to work it into every nook and cranny), and then flour it, tapping out any excess flour. I like the Nordic Ware Anniversary Bundt pan (get it on Amazon).
Combine the rum with the currants in a small saucepan. Set it on medium–low heat to soften the currants so that they plump with the warm rum. Take the pan off the heat and let the currants soak for 15 minutes while you prepare the cake batter.
Whisk together the flour, baking powder, nutmeg, and salt.
Using a stand mixer fitted with the paddle attachment, cream together the butter until creamy and smooth, 30 to 45 seconds.
Add the sugar in a steady stream and continue to beat on medium speed until light in colour and fluffy, about 5 minutes, stopping the mixer occasionally to scrape down the sides of the bowl.
With the mixer still on medium speed, add the eggs, 1 to 2 tablespoons at a time, beating after each addition until incorporated and stopping the mixer occasionally to scrape down the sides of the bowl. Add the vanilla and mix just until combined.
On the lowest speed, add the flour mixture in 3 additions alternately with the eggnog in 2 additions, beginning and ending with the flour mixture and mixing after each addition just until incorporated. Stop the mixer as needed to scrape down the sides of the bowl.
Using a rubber spatula, gently fold in the currants and any remaining rum.
Spoon the batter into the prepared pan and spread evenly with the spatula.
Bake the cake just until a cake tester inserted into the centre of the cake comes out clean, and the sides are beginning to come away from the pan, 60 to 65 minutes. Transfer the cake to a wire rack and let it cool in the pan for about 10 minutes while you prepare the glaze.