In a large bowl, weigh or measure the flour, baking soda, baking powder, cinnamon, nutmeg, and salt. I use a whisk to blend, then set aside. In another bowl, weigh or measure the granulated sugar and set it aside.
Mix the sugar and softened butter in a stand or hand-held mixer until blended, about 2 minutes on a medium mixer speed. Add pumpkin puree, egg, and vanilla extract and mix on a medium speed until combined.
On a low mixer speed, gradually add the flour mixture. Place the cookie dough into the refrigerator for 3 to 4 hours. You can place the cookie dough into the freezer for an hour to speed up the process. The dough is a little tacky, but if it is too loose, stick it back in the freezer for another 15 minutes.
Preheat the oven to 350°F (175°C or 180°C) and line your cookie sheet pans with parchment paper. Pull the cookie dough out of the refrigerator or the freezer and scoop out enough to make a 1-½-inch ball. I use a cookie scooper, but you could use a spoon. Try to make the balls about the same size so they bake evenly. Roll the balls in the confectioner sugar until coated. Place 12 sugar-coated balls on a prepared sheet pan.
Bake for 13-15 minutes at 350°F (175°C or 180°C); move to a cooling rack after you take them out of the oven.