Preheat oven to 375°F.

Place the butter, granulated sugar, and brown sugar in the bowl of a stand mixer. Beat on high until fluffy, about 3–4 minutes.

Add the vanilla and egg. Beat until incorporated, about 30 seconds.

Whisk together the flour, cream of tartar, salt, and baking powder in a medium sized bowl. With the mixer running on low speed, add the flour mixture to the butter mixture, ½ cup at a time. Continue to add the flour until it’s all incorporated.

Place the finely chopped pecans (I used my food processor to chop them) in a small bowl. Roll the dough into 1-inch balls. Roll the balls in the pecans and place the balls 2 inches apart on a parchment-lined baking sheet.

Bake for 8–9 minutes, or until the edges are light brown and the cookie no longer looks wet in the center.

Let cool for 5 minutes on the sheet pan. Remove the cookies and place on a wire rack to cool completely.