3 egg whites
1 1/2 teaspoon vanilla extract
Place egg whites and sugar in a (steel bowl that fits the mixer)double boiler over simmering water. Whisking constantly, cook until sugar has dissolved and mixture is warm (about 160 degrees).
Beat egg white mixture on high speed until it forms stiff fluffy peaks, beat until cooled( it will take about 8 mins). When completely cooled, add butter 1 tablespoon at a time, beating well on medium speed after each addition till all the butter is in. Add extract, mix on high till all the ingredients are well incorporated and smooth.
Makes about 2 1/2 cups - enough to frost a dozen cupcakes or a 6" cake.