Preheat the oven to 375 degrees F
In a large bowl cream butter, shortening, 1/2 sugar, and brown sugar together using an electric mixer
Mix in the egg and the vanilla.
Sift flour, cream of tartar, soda, and salt and add to creamed mixture. Mix well
Roll the dough into 1 1/4-inch balls. Dip the top half in cold water, and then in sugar.
Place cookies on the ungreased cookie sheet.
Bake in a preheated oven for10 to 12 minutes until the edge of the cookies should be lightly brown.
Remove from the oven and set on a cooling rack for a few minutes. Remove the cookies from the pan and set directly on the cooling rack and cool completely.