• Preheat the oven to 350 degrees. In a medium-sized mixing bowl, combine flour, baking soda, cream of tartar, and salt. Set aside.
• In a large mixing bowl, cream together butter, vegetable oil, sugar (1 1/4 C), powdered sugar, and water. Add in eggs.
• Slowly add in flour mixture until combined. Roll the dough into golf sized balls and roll in the reserved 1/2 cup of sugar before place onto a non stick cookie sheet.
• To give the cookies their signature rough edge, dip the bottom of a glass or flat measuring cup into the remaining sugar and press it onto the cookie ball to flatten the cookie. You still want the cookie to be thicker, so don't press them too thin.
• Bake for 8-10 minutes or until the bottom is lightly brown. The centers should be just barely baked as they will continue to bake while they cool. Don't overbake, or your cookies won't be nice and soft!

To Make the Frosting

• Cream together butter, sour cream, and salt. Add the powdered sugar. Add in the milk to the desired consistency. Spread over cooled cookies and store in an airtight container.