begin melting butter over medium heat in a sauce pan. Butter will begin to foam as it melts. wisk butter until it's golden brown in color and the smells nutty. (you'll be able to tell). Take butter off heat and set aside to cool in a small bowl

while butter is cooling, mix dry ingredients (flour, baking soda, pumpkin pie spice and cream of tarter. DO NOT add sugars)

in bowl of stand mixer add the brown and white sugars and melted butter. mix with paddle attachment on medium-low speed until combined. add egg and egg yolk, yogurt and vanilla. mix until combined well.

add flour mixture slowly and mix until just blended

wrap dough in plastic wrap and refrigerate for about 30 minutes.

preheat oven to 325°F

roll cookies into 1in balls and place 2in apart on cookie sheet. NOTE: you can also roll the balls in cinnamon and sugar mixture if you would like. (1/4 cup sugar 2 tablespoons Cinnamon)

bake for 8-11 minutes or until edges are lightly browned and centers are still very soft.