Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
Cream together the butter, granulated sugar, and brown sugar until light and fluffy.
Mix in pumpkin puree, egg yolk, and vanilla extract until smooth.
In a separate bowl, whisk together flour, baking powder, baking soda, cream of tartar, cinnamon, nutmeg, and salt.
Gradually add dry ingredients to wet ingredients, mixing until just combined. Fold in white chocolate chips.
In a small bowl, mix sugar and cinnamon for the coating.
Roll tablespoon-sized dough balls in the cinnamon-sugar mixture. Place on the baking sheet, spacing about 2 inches apart.
Bake for 10-12 minutes, until edges are lightly golden and centers are set.
Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
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