Spread your ½ cup of pumpkin with the back of a spoon over a triple layer of paper towels. This will absorb some of the moisture.
In a medium bowl add the flour, baking powder, pumpkin pie spice, cinnamon, and salt. Give it a whisk and set aside.
Combine butter and both sugars in the bowl of your kitchen-aid (or large mixing bowl) and mix on medium-high until well blended, 1 to 2 minutes. Add the pumpkin (just plop it from the paper towels into your bowl), egg, and vanilla and blend again until well combined.
Pour the flour mixture into the pumpkin mixture and mix until just combined. Fold in the white chocolate chips. Refrigerate 1 hour-ish to set.
Preheat the oven to 350 degrees. Line cookie sheets with parchment. Combine the ½ cup sugar and pumpkin pie spice + cinnamon on a plate. Use a small cookie scoop (about 1 ½ tablespoons) to scoop out balls of dough and place in sugar/spice mix. Roll the balls to coat completely and place on lined cookie sheets (12 per pan).
Cook 10 minutes. Remove and let cool a couple minutes before transferring to a cooling rack. These keep well for a few days, sealed.