1. Pour water to a depth of 1½ inches into a 3½-qt. saucepan over medium-high heat; bring to a boil. Reduce heat to medium, and simmer.
2. Combine first 3 ingredients in a 3-qt. heatproof bowl; beat at low speed with a handheld electric mixer until blended. Place bowl over simmering water, beating at high speed 7 minutes or until soft peaks form; remove from heat. Add vanilla. Beat to spreading consistency (about 3 to 5 minutes). Use immediately.