Preheat oven to 350 degrees. Line muffin pan with paper muffin liners.
In a medium bowl, mix together flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Set aside.
In a large mixing bowl, beat eggs until fluffy and pale in color. Add in sugar and butter, and continue beating for 1-2 minutes. Add in buttermilk and vanilla and mix well.
Add in the dry ingredients and mix until just combined, where no flour remains.
Scoop batter into muffin liners, filling about ⅔ full.
Mix together streusel sugars, flour, and spices together. Cut butter in with a pastry cutter. If you do not have a pastry cutter you can use your hands to combine it into the sugar mixture, until it is pea-sized crumbs. Stir in nuts, if using.
Scoop a heaping tablespoon onto the top of each muffin.
Bake for 18-23 minutes, until a toothpick inserted comes out clean.