Melt butter.  Add the sugar & mix with electric mixer.  Mix in eggs, vanilla, salt, cream of tartar.  Mix in flour.

Separate into 2 balls & wrap with plastic wrap.  Refrigerate 1 hour (or overnight).

Once chilled, roll out and cut into cookies.  Bake 350 degrees for 8 minutes (or until edges begin to lightly brown).  Cool on parchment paper or clean counter.  Ice and decorate after cool.

Frosting:

Melt Butter.  Add vanilla, milk, salt and whip with electric mixer.  Add powdered sugar until frosting is thick and spread-able.  If frosting gets too thick, thin with a little milk.