Boiled frosting- marshmallow !
pure vanilla extract
Mix sugar,cream of tartar, salt, egg whites and 1/4 cup of water in a pot or bowl over simmering water.
Beat steadily over low heat with a rotary or electric beater until the frosting stands in peaks, about 5 - 7 minutes, no more.(Thus the name: 7 minute frosting)
Add the vanilla just before spreading.
Makes enough to fill and frost an 8 or 9 inche two-layer cake.