A light and crisp sugar cookie made with real butter. This recipe is not too fussy, so it's fun to do with kids. If you don't have a decorative-bottom glass or cookie stamp, substitute something else, like a slotted spoon, a plastic thread spool with the paper removed, a potato masher, or anything that will give you an interesting pattern. As an alternative, you can roll walnut-size balls in decorative colored sugar (sanding sugar) or decorative sprinkles (jimmies), then flatten slightly with a spatula or plain-bottom glass.
Preheat oven to 350 degrees. Line cookie sheets with parchment, if desired.
In large mixing bowl, beat together butter, oil, and sugars until light and very fluffy. Add vanilla and beat well. Add soda, cream of tartar, and salt and mix thoroughly. Add flour a cup at a time and mix just until incorporated. Drop dough by rounded spoonfuls (use a small cookie scoop for uniformity) onto ungreased cookie sheet, about 1-1½ inches apart. Use a decorative-bottomed glass or cookie stamp to flatten each ball slightly, dipping the glass or stamp in sugar prior to each press.
Bake 10-12 minutes, until edges begin to turn golden brown. Cool 3 minutes on cookie sheet, then transfer to cooling rack to cool completely. Makes about 5 dozen cookies, depending on the size. Freeze indefinitely in an airtight container.