• Preheat oven to 350°F and lightly grease a cookie sheet. Set aside.
• In the stand of a mixer, cream together butter, oil, sugars, sour cream, and eggs. Mix until well combined and fluffy.
• In another bowl, combine flour, baking soda, cream of tartar, and salt. Slowly add to your creamed mixture and mix until combined.
• Roll dough into 1½ inch balls and place on a greased cookie sheet.
• Place ¼ cup sugar in a separate bowl. Lightly grease the bottom of a glass with cooking spray. Dip the bottom of the glass into the sugar and then press down onto each dough ball to make it about 3 inches in diameter to give the cookies their cracked edges.
• Bake for 8-9 minutes and let sit on the cookie sheet for 5 minutes before removing to a cookie rack.

Frosting

• While the cookies are cooling, cream the butter, powdered sugar, 1 drop of food coloring, and vanilla extract. Mix well and add the desired amount of milk to get it the desired thickness. I add 3-4 tablespoons.
• Spread frosting on cookies right before serving.