Preheat oven to 350°F, grease a 9"x9" square pan
In a bowl, mix together flour, baking powder, baking soda, salt, cinnamon and nutmeg. Set aside.
In a large mixing bowl, cream the butter and sugar until light and fluffy.
Add eggs, pumpkin puree, sour cream and vanilla. Mix until smooth.
Gently add dry ingredients, mixing until just incorporated.
Pour batter into prepared pan.