Preheat oven to 350˚F.
Line two baking sheets with parchment paper and set aside.
In a large bowl, beat 2 cups butter with an electric mixer set on medium speed until light and fluffy.
Add granulated sugar, baking powder, baking soda, salt, cinnamon, and nutmeg. Beat until combined, scraping bowl occasionally.
Add eggs and 2 teaspoons vanilla; beat until combined.
Beat in pumpkin.
Add the flour slowly until combined. Dough will be wet.
Drop dough by the tablespoon onto previously prepared baking sheets, two inches apart.
Bake in the preheated oven for 10 to 12 minutes, or until tops are set.
Remove from oven and transfer cookies to a wire rack; let cool.
While the cookies cool, beat all of the frosting ingredients in a separate bowl until soft and whipped.
Frost cooled cookies and sprinkle with cinnamon.
Serve, or store in airtight containers and keep at room temperature for up to 5 days.