Preheat oven to 375°F. Line a standard muffin tin with paper liners.
To make the streusel topping, combine the flour, sugar, and nutmeg in a small dish. Add the melted butter and mix until crumbly. Set aside.
In a large bowl, whisk together eggnog or half & half, eggs, melted butter, and extracts. In a medium bowl, combine flour, sugar, baking powder, ground nutmeg, and salt. Add the dry mixture to the wet mixture and stir well with a spoon until evenly combined.
Portion the batter evenly into the prepared muffin tin. Top each muffin with the streusel topping.