Blot the ½ cup pumpkin puree by spreading it on a plate lined with paper towels. Fold paper towels over the top and gently press down for 30 seconds. Repeat this 3–4 times, replacing wet towels each time, until the pumpkin volume reduces by almost half and resembles a thick paste. Checkpoint: Your blotted pumpkin should measure about ¼ cup and feel dense, not watery.

In a large mixing bowl, pour the melted, slightly cooled ½ cup butter. Add the ½ cup granulated sugar and ½ cup packed brown sugar. Whisk vigorously for 1–2 minutes until the mixture is smooth and pale. Checkpoint: The mixture should look light and slightly fluffy, not separated.

Whisk the blotted pumpkin paste into the butter-sugar mixture for 1 minute. Add the 1 large egg yolk and 1 tsp vanilla extract. Whisk for another 1–2 minutes until everything is completely combined and no streaks of pumpkin remain. Checkpoint: The wet mixture should look uniform, orange-tinted, and creamy.

In a separate medium bowl, whisk together 1 ½ cups all-purpose flour, 1 ½ tsp cream of tartar, ½ tsp baking soda, ¼ tsp fine sea salt, 1 tsp pumpkin pie spice, and ½ tsp ground cinnamon. Whisk for 30 seconds to combine and aerate. Checkpoint: The dry mixture should look evenly blended with no lumps of cream of tartar.

Pour the dry ingredients into the wet ingredients. Using a rubber spatula, fold gently for 2–3 minutes, scraping the bottom and sides of the bowl, just until no white flour streaks remain. Do not overmix or stir vigorously—the dough should be thick and slightly lumpy. Checkpoint: No flour should be visible, but the dough should look slightly undermixed compared to typical cookie dough.

Cover the bowl tightly with plastic wrap. Place it in the refrigerator for at least 45 minutes—or up to 2 days. This resting time is mandatory; the dough will be too sticky to scoop without chilling. Checkpoint: The dough should be firm and hold its shape when scooped, not wet or runny.

Position your oven racks to the upper-middle and lower-middle positions. Preheat the oven to 350°F (175°C) for 15 minutes. Line two large baking sheets with parchment paper and set aside. Checkpoint: The oven should beeping or displaying 350°F, and the parchment should be flat on the sheets.

In a small shallow bowl, mix ¼ cup granulated sugar and 1 ½ tsp ground cinnamon. Stir with a fork for 30 seconds until the cinnamon is evenly distributed. Checkpoint: The coating should look uniform, not streaky, and smell strongly of cinnamon.

Remove the chilled dough from the refrigerator. Using a 1.5-tablespoon cookie scoop or a tablespoon measure, scoop one portion of dough and drop it into the cinnamon-sugar bowl. Roll it gently in the coating, pressing and turning to coat all sides generously for about 20 seconds. Checkpoint: Each ball should look completely covered in the cinnamon-sugar mixture, not patchy.

Place the coated dough ball on a prepared baking sheet. Repeat scooping and coating the remaining dough, placing each ball about 2 inches apart. You should have 12–14 cookies total. Checkpoint: All balls should be evenly spaced and generously coated.

Transfer both baking sheets to the preheated 350°F oven, placing one on the upper-middle rack and one on the lower-middle rack. Bake for 10–12 minutes. The cookies are done when the edges appear set and dry, but the centers still look very soft and slightly underbaked. The tops may crack slightly. Checkpoint: Press the center of one cookie gently with your finger—it should feel soft and spring back slightly, not firm or hard.

Remove both baking sheets from the oven. Let the cookies cool on the baking sheets for exactly 10 minutes—do not move them during this time. They will continue to set as they cool. Checkpoint: The cookies should look slightly firmer on top but still soft in the center when you gently press them.

After 10 minutes of cooling on the sheet, transfer each cookie to a wire cooling rack using a thin spatula. Handle gently, as they are still delicate. Let them cool completely for another 20–30 minutes on the rack. Checkpoint: Cookies should now feel set on the outside but still have a slight chew when bitten.