Preheat and Prep: Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.
Whisk Dry Ingredients: In a medium bowl, whisk together the flour, baking soda, cream of tartar, salt, cinnamon, nutmeg, and ginger. This ensures the spices are evenly distributed throughout the dough.
Cream Butter and Sugar: In a large bowl, use your electric mixer to cream the softened butter and 1 1/2 cups of granulated sugar together until the mixture is light, fluffy, and pale in color (about 2-3 minutes). This incorporates air for a tender cookie.
Add Wet Ingredients: Add the pumpkin puree, egg, and vanilla extract to the butter mixture. Mix on low speed until well combined. The mixture might look a little separated — that's totally fine.
Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Overmixing will develop the gluten and make the cookies tough.
Fold in White Chocolate: Use a rubber spatula to gently fold the white chocolate chips into the dough until they are evenly distributed.
Make the Coating: In a small bowl, stir together the remaining 1/4 cup of granulated sugar and 1 tablespoon of ground cinnamon.
Scoop and Roll: Using a cookie scoop, scoop tablespoons of dough and roll them into balls. Roll each ball generously in the cinnamon-sugar mixture. Place them on the prepared baking sheets, spacing them about 2 inches apart.
Bake: Bake for 10-12 minutes. The edges should be lightly golden and set, but the centers will still look slightly soft and puffy. For softer cookies, stick to the 10-minute mark.
Cool and Serve: Let the cookies cool on the baking sheet for 5 minutes. This allows them to set up properly. Then, transfer them to a wire rack to cool completely. The centers will fall slightly, creating that perfect crinkly top.