In a medium bowl, whisk together flour, baking powder, salt, spices and set aside. In a small bowl, combine the pumpkin puree and orange zest. Also set aside.
In a bowl of an electric mixer set on medium high speed, cream the butter and sugars until fluffy, about 2-3 minutes. Add the pumpkin puree mixture and mix well. Add the egg and vanilla extract, scraping down sides of the bowl to incorporate all of the ingredients.
Reduce the mixer speed to low and add flour mixture into liquid in two to three parts. Mix just until incorporated.
Cover dough with plastic wrap and chill at least an hour, or until dough becomes slightly firm.
When ready to bake, preheat oven to 350°F.
Line a couple of baking sheets with parchment paper (or spray with nonstick spray). Mix spiced sugar mixture ingredients in a small bowl.
Remove cookie dough from refrigerator. Use a small cookie scoop (1 – 1 1/2 teaspoon) or a small spoon to scoop out dough and roll into balls. Use your hands to roll the balls in the spiced sugar making sure they're coated really well. Place 2 inches apart on the prepared baking sheets. If desired, use a glass with a nice, flat bottom to flatten the balls. Unless you like your snickerdoodles puffy. We like ‘em puffy. Sprinkle some additional sugar on top of the flattened cookies.
Bake the cookies for 10 to 14 minutes, or until they are slightly firm to the touch. Let cool on baking sheets for 5 minutes or so, and then remove them to a wire rack to cool completely.