Prepare the Pan: Preheat oven to 350°F and line a 9×5-inch loaf pan with parchment paper.
Mix Dry Ingredients: Combine flour, pudding mix, baking powder, salt, nutmeg, and allspice in a medium bowl.
Cream Wet Ingredients: Beat butter, sugar, eggs, eggnog, vanilla, and rum extract until smooth.
Combine Wet and Dry: Mix dry ingredients into wet just until combined.
Bake: Pour into pan and bake for 55–60 minutes, tenting with foil if browning too quickly.
Cool: Let cool in pan 10 minutes, then on wire rack until fully cooled.
Make Glaze: Whisk powdered sugar, rum extract, nutmeg, and eggnog until smooth; add milk as needed.
Glaze and Serve: Spoon glaze evenly over loaf and allow to set before slicing.
