Butter 2 baking sheets and dust with flour.
Mix (on high sped) egg whites and cream of tartar to a thick foam.
Continuing to beat, add sugar and whip until meringue holds very stiff peaks.
Beat in vanilla.
Spoon meringue into a pastry bag fitted with a 1/2-in. plain tip. Pipe meringue onto baking sheets into ghostly shapes about 1/4 - 1/2 in. thick, 2 - 4 in. wide, and 4 - 6 in. long, spacing about 2 in. apart.
To make eyes (noses and mouths, if desired) press chocolate chips lightly into meringue.
Bake in a 200 degree oven until meringues begin to turn pale gold and are firm to touch, about 90 mins.
Switch pan positions halfway through baking.
Turn off heat and leave meringues in closed oven for 1 hour.