Sift together flour, soda and cream of tartar. Stir in the salt. Set aside.
In a mixing bowl, beat butter, oil, and both sugars until creamy. Beat in vanilla, lemon juice and nutmeg (or zest). Beat in egg.
With a mixing spoon, stir the flour mixture into the butter mixture until well mixed. If dough is soft, cover and chill for 1 hour.
Drop dough by rounded teaspoonfuls (or a #70 scoop) onto an ungreased baking sheet or a baking sheet lined with parchment. Dip bottom of a flat glass in sugar and press cookies down to make circles. Bake for 12 minutes or until edges or nicely browned.
Notes
If you don't have a scale, make sure to stir and aerate your flour and then scoop it into the cup. If you use too much flour the cookies will not be as crisp. Also, the yield may vary depending on how big you actually make the cookies. You should get over 3 dozen.