• In a large mixing bowl, cream together the butter, oil, white sugar and powdered sugar until well combined and fluffy. Add eggs and vanilla, mix well.
• In a medium bowl, whisk together flour, cream of tartar and soda. Gradually add dry mixture to wet ingredients, until well combined.
• Transfer dough to smaller bowl, cover with plastic wrap and chill at least 2-3 hours, overnight is best.
• Preheat oven to 350°F. Roll dough into balls and place on cookie sheet. Dip the bottom of a glass into water then slightly flatten balls.
• Sprinkle with colored sugar if desired. Bake for 10-12 minutes or until slightly golden brown. Cool slightly on rack then remove. Store in airtight container.

Frosting Directions

• To make the frosting, beat the butter for 2 or 3 minutes until fluffy. Beat in the powdered sugar and vanilla and enough of the milk or cream to make a spreadable consistency. Tint the frosting whatever color is desired.