Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and grease a small loaf pan.
In a large bowl, whisk together flour, granulated sugar, baking powder, nutmeg, and salt.
In a separate bowl, whisk the eggnog, egg, melted butter, and vanilla extract.
Gently fold the wet ingredients into the dry ingredients until just combined.
In a small bowl, combine brown sugar, topping flour, cold butter, and topping nutmeg using a fork until crumbly.
Pour batter into the prepared loaf pan and sprinkle the crumb topping evenly over the surface.
Bake for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack.