In a large bowl, cream ¼ cup unsalted butter together with ¼ cup light brown sugar and ½ cup white sugar for 2 minutes.
Add 1 egg and beat until well incorporated. Add 1 teaspoon vanilla extract and ¾ cup pumpkin puree and mix. It might look curdled and that is fine.
Add the sifted dry ingredients (1 ¼ cups all-purpose flour, 1 teaspoon baking powder, ¼ teaspoon baking soda, 1 ½ teaspoons pumpkin pie spice and ¼ teaspoon salt) to the wet ingredients in 2 parts, stirring until just combined. Don't skimp on the spices, or the cookies will not have that deep flavor we love. You can use up to 2 teaspoons. Avoid overmixing. You can sift them before or have the ingredients measured and sift them directly over the butter mixture (my choice).
Cover the bowl with plastic wrap and chill the cookie dough in the refrigerator for at least 1 hour or up to 3 days.
Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.
Scoop out walnut-sized portions of the chilled dough and roll them into balls. The dough might still be somewhat soft and sometimes the balls will be slightly irregular. That is fine.
Roll each ball in 1 cup powdered sugar, coating it generously, and place on the prepared baking sheets, leaving 1 inch or more between them. Don't shake them to remove excess sugar; they must be thickly coated.
Bake for 10-12 minutes or until the edges are set, but the centers are still soft.
Allow the cookies to cool on the baking sheet for a few minutes on a cooling rack before transferring them to the wire rack to cool completely.
Notes
Baking time: consider that all ovens and pans are different, even if they look similar. The baking time in my recipes is as accurate as it can be, but it might take you more or less time. You can use a thermometerto check that your oven is at the right temperature. I recommend you keep track of how your oven works and what tiny details you might need to adjust. Storage: Room temperature: store the cooled cookies in an airtight container for up to a week. Freezing: for longer storage, freeze the cookies in a single layer and then transfer them to a freezer bag. Thaw frozen cookies at room temperature before serving. Cookie dough: it can be kept in the fridge for 3-5 days before baking. Cover the bowl well with plastic wrap. Frozen dough: you can form the balls, place them on a cookie sheet and freeze them until rock solid. Bake directly from the freezer.