Best Sugar Cookie

Cookies - In a large bowl with an electric mixer, cream together the butter and sugar until the mixture is light and fluffy. Beat in the vanilla and eggs. In a separate bowl, sift together the flour, cream of tartar, baking soda and salt. Gradually add the flour mixture to the butter mixture, stirring until the mixture forms a dough. Chill, covered, for at least two hours, or overnight. Working quickly, roll out the dough ⅛ inch thick on a lightly floured surface and, using a 3 inch cutter, cut out the cookie rounds. Transfer the rounds to an ungreased baking sheet and bake in batches in the middle of a preheated 350 degree oven for 6 to 8 minutes, or until pale golden. Transfer the cookies to a rack and let cool. Mix all icing ingedients together and spread on cooled cookies.