In a medium heat proof bowl over simmering water, whisk together egg whites, sugar and cream of tartar. Continue whisking until sugar has dissolved completely and egg whites are warm to the touch. Transfer to a stand mixer, with whisk attachment, whisk on medium-high speed until stiff peaks form. Mix in vanilla in the last 30 seconds. Transfer mixture to a large piping bag
fit with desired piping tip. Alternately a large plastic bag may be used with the tip snipped off.