In a large bowl using a spatula, combine melted/cooled butter and sugars until well-combined. Add pumpkin puree; mix until combined.
Add egg yolk and vanilla extract; mix until combined.
Gradually, add flour mixture to wet ingredients and mix until well-combined.
Cover and refrigerate dough for a minimum of one hour. Dough can be refrigerated overnight for up to five days.
Preheat oven 350 degrees.
In a small bowl, mix together ¼ cup granulated sugar and 2 teaspoons of cinnamon.
Scoop chilled dough into 1 ½ tablespoon balls, or use a #40 disher to scoop balls of dough. Roll balls of dough in the sugar-cinnamon mixture, and place on a silicone mat/parchment paper-lined baking sheet; spacing 2" apart. Keep dough chilled in between batches.
Bake for 10-12 minutes. Do not place cookie dough on hot baking sheet.
Allow cookies to cool completely on baking sheet. Eat & Enjoy!
Notes
Pumpkin Snickerdoodles should be stored in an airtight container and will keep 4+ days.