In a bowl of an electric mixer with the whisk attachment, beat egg whites and cream of tartar together until light and frothy.
With the mixer running, slowly pour in 2 Tbls sugar.
Beat until soft peaks form.
In a small saucepan, combine water, corn syrup, and 2/3 c sugar.
Cook over medium heat until boiling.
Cook, stirring, until mixture reaches the firm-ball stage, about 242 to 248 degrees on a candy thermometer, about 6 minutes.
Immediately remove from heat.
With the mixer on low, slowly add hot syrup to egg white mixture.
Increase mixer speed to high and continue beating for 5 min.
Add vanilla and continue to beat until mixture looks like marshmallow cream, about 1 minute more.