Gather all ingredients and measure them into separate bowls—this ensures you won't miss anything and the baking process flows smoothly. Place your egg yolk in a small bowl to come to room temperature if needed (this helps it incorporate better into the dough). Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. While the oven heats, you can move forward with mixing the dough.

In a large mixing bowl, beat together the softened unsalted butter, sugar, and packed brown sugar until the mixture is light and fluffy—this takes about 2-3 minutes and is important for creating a tender cookie texture. Add the pumpkin puree and mix until fully incorporated. The mixture may look slightly separated at first, but continue mixing until it comes together smoothly. I like using Kerrygold butter here because its rich, slightly salted flavor really complements the pumpkin spice beautifully.

Add the room-temperature egg yolk to your pumpkin-butter mixture and beat until fully incorporated. Pour in the vanilla extract and mix until the wet mixture is completely homogeneous. This creates a smooth base that will help distribute the spices evenly throughout the dough.

In a separate bowl, whisk together the flour, pumpkin pie spice, baking soda, cream of tartar, and salt. I always measure the pumpkin pie spice fresh from a jar rather than using pre-measured packets—the flavor is noticeably more vibrant. Add the dry ingredient mixture to your wet mixture in one addition, then fold and stir until just combined. Don't overmix; the dough should come together without any visible streaks of flour, but you want to avoid developing too much gluten, which can make the cookies tough.

Cover the dough (use plastic wrap or transfer to a covered bowl) and refrigerate for 45 minutes. This resting period allows the flavors to meld, makes the dough easier to handle, and helps the cookies spread less and bake more evenly. While the dough chills, your oven should be preheated and ready.

In a small shallow bowl, whisk together the 1/4 cup sugar and ground cinnamon. Set this aside near your work station so you can quickly roll each cookie ball in the coating. Freshly ground cinnamon makes a noticeable difference in flavor here, so I grind my own whenever possible.

Remove the chilled dough from the refrigerator and scoop it into 1 1/2 tablespoon-sized balls (a cookie scoop makes this quick and consistent). Roll each ball in the cinnamon sugar mixture until fully coated, then place on your prepared baking sheet about 2 inches apart—these cookies will spread slightly as they bake. Bake at 350°F for 10-12 minutes, until the edges are set but the centers still have a slight jiggle when you gently shake the pan. Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.