In a large bowl or stand mixer, cream the butter until it is light and fluffy, at least 2 minutes. Add the 2 cups brown sugar and continue beating for 1 minute, scraping the sides and bottom of bowl.
Add 2 eggs and vanilla extract. Beat well.
Add the flour on top of the mixture but don't mix it in.
Use a small spoon to stir the baking powder, 1 and 1/2 teaspoons cinnamon, nutmeg, and salt into the flour.
Beat the flour mixture in until barely combined. Once the flour streaks are gone you're done. Make sure to scrape the sides and bottom.
Use a spatula to scrape the dough (it's a very sticky dough) into the prepared pan. You can grease your hands or spatula with nonstick spray to press it down, or get your hands a little wet. Smooth the surface.
In a small bowl, combine 2 tablespoons sugar with2 teaspoons cinnamon. Sprinkle this mixture evenly over the top of the pan. Pat it down with your hands a little bit.
Bake at 350 for 25-30 minutes, until a toothpick comes out of the center with no batter stuck to it.
Source: I lightly adapted this recipe is from my mother-in-law Kris, who got it from Food.com.