Combine the flour, baking powder, baking soda, cinnamon, and salt in a mixing bowl and whisk to combine. Set aside. Place the butter and both sugars in a separate mixing bowl and beat to combine. Add the eggs and beat well.
Add half of the dry ingredients to the wet ingredients and beat to combine. Slowly add the buttermilk while beating, and then add the remaining dry ingredients. Spread the mixture in a well-greased 9x13-inch pan.
Combine the brown sugar, pecans, cinnamon, and nutmeg for the topping in a small bowl. Sprinkle on top of batter in the cake pan, taking care not to pile too much in the center.
Cover the pan with a lid or with foil and refrigerate overnight. Bake in a pre-heated 350°F oven for 45-50 minutes, until a toothpick inserted comes out clean or with moist crumbs.
Notes
This recipe can be halved for a smaller recipe. Bake in a 9-inch pan.