Preheat the oven to 350 degrees F. Line a muffin pan with paper liners or spray with cooking spray. The recipe makes 10 muffins. Set aside.
First make the streusel topping. In a small bowl, combine flour, brown sugar, cinnamon, and nutmeg. Add the butter and rub together with your fingers until mixture looks like coarse crumbs. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, cinnamon, nutmeg, and salt. Set aside.
In a medium bowl, combine eggnog, egg, melted butter, and vanilla extract. Whisk until smooth. Pour the liquid ingredients over the dry ingredients and stir until just combined. Don't over mix.
Place 1 tablespoon of muffin batter in each prepared muffin cup. Top with 1 teaspoon of streusel. Add more batter to cover the streusel, about a heaping teaspoon. Top muffins with remaining streusel.
Bake muffins for 20 minutes, or until a toothpick inserted in the center comes out clean. Remove from oven and let muffins cool to room temperature.
While the muffins are cooking, make the eggnog glaze. In a medium bowl, whisk together powdered sugar, eggnog, and pinch of nutmeg. Whisk until smooth. Drizzle glaze over the muffins. Serve and enjoy!