Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper and set them aside.
Whisk the dry ingredients: In a medium bowl, whisk together the flour, baking soda, cream of tartar, salt, cinnamon, nutmeg, and ginger. Set this aside while you work on the wet mixture.
Cream the butter and sugar: In a large bowl, beat the softened butter and 1 1/2 cups sugar together until the mixture is light, fluffy, and pale yellow — about 2 to 3 minutes. Scrape down the sides of the bowl.
Add the wet ingredients: Mix in the pumpkin puree, the egg, and the vanilla extract until everything is fully combined. The mixture might look a little curdled or separated — that's totally normal. Don't panic.
Combine wet and dry: Gradually add the flour mixture to the wet ingredients, mixing on low speed until just combined. Over-mixing here will make the cookies tough. Stop when you can't see any more dry flour.
Fold in the white chocolate: Use a spatula to gently fold in the white chocolate chips. The dough will be soft and a little sticky — that's exactly what we want.
Make the coating: In a small bowl, stir together the remaining 1/4 cup sugar and 1 tablespoon cinnamon.
Scoop and coat: Use a 1.5-tablespoon cookie scoop to portion the dough. Roll each portion into a smooth ball, then roll it generously in the cinnamon-sugar mixture. Place the coated dough balls on the prepared baking sheets, spacing them about 2 inches apart.
Bake: Place the sheets in the preheated oven and bake for 10 to 12 minutes. You'll know they're done when the edges are lightly golden and the centers look just set — they should still be soft and slightly puffed.
Cool: Let the cookies cool on the baking sheet for 5 minutes. This allows them to set up properly. After 5 minutes, transfer them to a wire rack to cool completely (or serve warm — I won't tell).