Preheat oven to 350 degrees F and line two cookie sheets with parchment paper.
Place the butter into a medium saucepan over medium heat. Let the butter cook while occasionally stirring to ensure the butter is cooking evenly.
1 cup unsalted butter
Cook the butter until it is a golden brown color and smells nutty and toasted, about 5 -7 minutes. Remove the pan from the heat.
Let the butter cool to room temperature.
Combine the flour, cream of tartar, baking soda, salt and pumpkin spice in a medium bowl and whisk to combine.
2 ½ cups all purpose flour, 2 teaspoons cream of tartar, 1 teaspoon baking soda, ½ teaspoon fine sea salt, ½ teaspoons pumpkin spice
In the bowl of a stand mixer, combine the brown butter, granulated sugar, and brown sugar. Beat on medium speed for 2 minutes until well blended.
½ cup granulated sugar, 1 cup light brown sugar, packed
Beat in the egg, egg yolk, vanilla, and pumpkin purée.
1 large egg, room temperature, 1 large egg yolk, room temperature, 2 teaspoons pure vanilla extract, 2 tablespoons pumpkin purée
On low speed, add the flour mixture, beating just until incorporated.
Scoop the dough with a medium size/2 tablespoon ice cream scoop onto a lined cookie sheet.
Whisk together the granulated sugar and pumpkin spice.
¼ cup granulated sugar, 1 ¼ teaspoons pumpkin spice
Roll each dough ball in the sugar mixture until coated. Use the bottom of a cup or measuring cup to flatten the cookies just a bit.
Bake for 9-11 minutes or until the edges are lightly brown and the tops look just set. Transfer to cookie sheets to wire racks to cool, then serve.