Preheat and prep pans: Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper for easy release and cleanup.

Drain the pumpkin slightly: Spoon pumpkin purée onto a few layers of paper towel, fold over, and press gently to remove excess moisture for 1–2 minutes. This keeps the cookies from turning cakey.

Cream the butter and sugars: In a large bowl, beat softened butter, brown sugar, and granulated sugar until light and fluffy, about 2 minutes. This step builds structure and makes a better crumb.

Add wet ingredients: Mix in the egg yolk, vanilla extract, and the blotted pumpkin purée until smooth. Scrape down the bowl to prevent streaks.

Combine dry ingredients: In a separate bowl, whisk flour, baking soda, cornstarch, salt, cinnamon, and pumpkin pie spice. Stir in the rolled oats.

Bring the dough together: Add the dry mixture to the wet ingredients and mix on low just until combined. Fold in chocolate chips (and nuts, if using). Do not overmix.

Chill the dough: Cover the bowl and chill for 20–30 minutes. This relaxes the dough and keeps the cookies thick and chewy.

Scoop and bake: Scoop 1.5-tablespoon mounds of dough and space them about 2 inches apart. Bake for 10–12 minutes, until the edges look set and the centers are slightly soft.

Finish and cool: If you like, press a few extra chocolate chips on top right out of the oven and sprinkle with a pinch of flaky salt. Let the cookies cool on the sheet for 5 minutes, then move to a rack to finish cooling.

Serve: Enjoy warm for melty chocolate and soft centers, or at room temperature for a chewier bite.