Cream together 1/2 cup room temperature butter, 1 cup sugar, and vanilla pudding mix in a large bowl until smooth and creamy.
Beat in eggnog, eggs, vanilla extract, and rum extract until well combined.
In a separate bowl, whisk together flour, baking powder, salt, and nutmeg.
Gradually add the dry ingredients to the wet mixture and stir until just combined, avoiding overmixing.
Grease and flour four mini loaf pans and evenly divide the batter among them, smoothing the tops.
Combine cold cubed butter, cinnamon, nutmeg, flour, and sugar for the crumb topping in a small bowl.
Use a fork to mix the crumb topping until crumbly and sprinkle it evenly over the batter in each pan.
Bake at 350°F (175°C) for 35-40 minutes or until a toothpick inserted in the center comes out clean.
Cool the loaves in the pans for 10 minutes, then transfer to a wire rack to cool completely.