In a medium bowl, whisk together the flour, baking soda, salt, pumpkin pie spice, and cinnamon. Set aside.

Measure 200g (¾ cup + 1 tablespoon) canned pumpkin puree and spread it over several layers of paper towels. Gently blot away excess moisture, replacing the paper towels as needed, until the pumpkin weighs approximately 110g. Do not squeeze the pumpkin completely dry. A small variation in the final weight is fine.

In the bowl of a stand mixer fitted with the paddle attachment, or using a hand mixer, beat the softened butter, brown sugar, and granulated sugar on medium speed for about 2 minutes, until smooth and creamy.

Add the egg yolk and vanilla extract and beat until fully incorporated.

Add the sourdough discard and blotted pumpkin and mix until combined.

Add the dry ingredients and mix on low speed just until no dry streaks remain. Do not overmix.

Cover the dough and refrigerate for at least 30 minutes, or until firm enough to scoop and shape. The dough can also be refrigerated overnight.

When ready to bake, preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.

Use a #40 cookie scoop or a medium cookie scoop to portion approximately 1½ tablespoons of dough per cookie. Roll each portion between your palms to form a smooth ball and place about 2 inches apart on the prepared baking sheets.

For the most uniform cookies, place a small piece of parchment paper over each dough ball and gently press with the flat bottom of a measuring cup or glass until the cookie is approximately ⅓ inch thick. This method creates a rounder, more evenly shaped cookie. If you prefer thicker cookies, you can gently flatten the dough with your hand instead.

Bake for 9–10 minutes, checking the cookies at 8 minutes. The edges should be set while the centers remain soft but no longer appear wet. The cookies should not brown significantly.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.