Preheat oven to 350 and line several half sheet pans or cookie sheets with parchment paper.

In the bowl of a stand mixer fitted with the paddle attachment, add butter, oil, sugar and powdered sugar. Sprinkle baking soda, cream of tartar and salt across the top. (You don’t want this all in one spot!) Mix until well combined and super creamy, about 1-2 minutes, scraping down the sides of the bowl as needed. (I often cover my mixer with a towel so the sugar or flour doesn’t send up dust.)

Add sour cream, eggs and vanilla and mix until well combined for about 1-2 minutes, scraping down sides of bowl as needed.

Add the flour and mix until mixture is evenly mixed and flour is distributed equally.

Scoop the dough into large rounded tablespoons and roll into balls. Place several inches apart on prepared baking sheets. (I usually do 5 rows of cookie dough distributed with 4 cookies in row 1, two cookies in row two, then 4, then two, then four so I can get 16 to 18 cookies on a cookie sheet.)

Place several inches apart. Place about 1.2 c of sugar in a bowl. Spray the bottom of a flat bottomed glass with cooking spray and dip into sugar. Press each cookie into an even thickness about 1/4 to a 1/2″ thick. Do this with each cookie, but no need to spray the glass each time.

Bake the cookies for 10 – 12 minutes or until just set. Do not let them get too golden on the edges or the bottom unless you like a dry and crumbly cookie. I prefer mine creamy and soft so I only baked them about 11 minutes.

Let them cool a few minutes before removing to a cooling rack to cool completely.

Make the frosting while these are baking. Rinse out the bowl of the mixmaster and combine butter, sour cream, and vanilla. Mix until thick and smooth, about 1-2 minutes. Add the powdered sugar and milk or cream and mix until well combined and creamy, adding more milk as needed. (Just add small spoonfuls at  time.)

Frost the cooled cookies and sprinkle as desired!