In a large mixing bowl, cream together ½ cup of room temperature salted butter and 1 cup of sugar until the mixture is light and fluffy, about 3-5 minutes. Add in the instant vanilla pudding mix, 1¾ cups of chilled eggnog, 2 room temperature eggs, 1 teaspoon of vanilla extract, and ½ teaspoon of rum extract if using. Mix until everything is evenly combined and smooth.

In a separate bowl, whisk together 2¼ cups of all-purpose flour, 2 teaspoons of baking powder, ¼ teaspoon of salt, and ¼ teaspoon of freshly grated nutmeg. Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined.

Preheat your oven to 350°F (175°C) and grease and flour four mini loaf pans. Divide the batter evenly among the prepared pans.

In a small bowl, mix together ¼ cup of cold, cubed butter, ½ cup of all-purpose flour, ½ cup of sugar, ½ teaspoon of cinnamon, and ¼ teaspoon of nutmeg until the mixture resembles coarse crumbs. Sprinkle it over the batter in each loaf pan.

Place the filled loaf pans in the preheated oven. Bake for 35–40 minutes, or until the tops are golden brown and a toothpick inserted in the center comes out clean.

Once baked, remove the pans from the oven and let them cool in the pans for about 10 minutes. Carefully transfer the loaves to a wire rack to cool completely.