Marshmallow Frosting

Place egg whites, sugar and cream of tartar in a heatproof bowl. Set over a saucepan with simmering water. Whisk constantly until sugar is dissolved and whites are warm to the touch, approximately 3 to 4 minutes.

Remove from saucepan and place on bench. Beat with an electric mixer on low speed until stiff glossy peaks form (around 5 to 7 minutes). Add vanilla and mix until combined. Use immediately.