Preheat oven to 350F and line a baking sheet with parchment paper.
Using a handheld mixer, cream butter, oil, and both sugars until creamed.
Add baking soda and cream of tartar and mix for 1 to 2 minutes, until creamy.
Beat in sour cream, eggs, and vanilla extract for another 1 to 2 minutes, until smooth.
Add flour and stir just until combined.
Add 1/2 cup of sugar to a bowl and spray the bottom of a glass with non-stick cooking spray.
Dip the glass in the sugar and press the cookies to about a 1/2" thickness, re-dipping the glass after each cookie.
Bake until cookies are only just set and not golden on the edges; about 10 to 12 minutes.
Cool for at least 5 minutes on the baking sheet before transferring to a wire cooling rack to cool completely.