Preheat oven to 350° F. Lightly grease and/or line a 9×13 inch pan. Combine the flour, baking powder, cinnamon, nutmeg and salt and set aside.
In a large bowl, beat together butter and brown sugar for 3-5 minutes. Add in the eggs one at a time, then the vanilla, and beat until smooth.
Stir in the flour mixture until well blended. Spread evenly in prepared pan (mixture will be somewhat like a cookie batter, so it’s best to spread it out with a greased spatula or your hands). Combine the granulated sugar, cinnamon, and nutmeg in a little bowl. Evenly sprinkle cinnamon sugar mixture over the top of the batter.
Bake 25-30 minutes or until the surface springs back when gently pressed. Cool before cutting.