Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper to prevent sticking and make cleanup easier.
Place the pumpkin puree on several layers of paper towels and gently blot away excess moisture. This step helps prevent the cookies from becoming too cakey or spreading unevenly.
In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar until the mixture looks creamy and well combined. This usually takes about 2–3 minutes using an electric mixer.
Mix in the pumpkin puree, egg yolk, and vanilla extract. Stir until everything is evenly incorporated. The mixture may look slightly separated at first, but it should become more uniform as you mix.
In another bowl, whisk together the flour, cinnamon, pumpkin pie spice, baking soda, baking powder, salt, and cornstarch. Mixing the dry ingredients separately helps distribute the spices and leavening agents evenly.
Gradually add the dry ingredients to the wet mixture. Stir gently until a soft dough forms. Avoid overmixing, as excessive mixing can make the cookies tougher.
Fold the white chocolate chips into the dough using a spatula. If desired, reserve a small handful of chips to press onto the cookie dough just before baking.
Cover the bowl and refrigerate the dough for approximately 30 minutes. Chilling helps the dough firm up and can reduce excessive spreading during baking.
Scoop approximately 1½ tablespoons of dough for each cookie and place the portions on the prepared baking sheets, leaving about 2 inches between them. Press a few extra white chocolate chips onto the tops for an attractive finish.
Bake for 12–14 minutes, or until the edges are set and the centers still look slightly soft. Avoid waiting for the entire cookie to become firm in the oven, as the cookies will continue to set while cooling.
Allow the cookies to rest on the baking sheet for 5–10 minutes before transferring them to a wire rack. Let them cool further before storing them in an airtight container.Enjoy your soft, warmly spiced White Chocolate Pumpkin Cookies with a glass of milk, a cup of tea, or your favorite coffee.