- Using a double boiler method, whisk egg whites and sugar in the mixer bowl. Place over boiling water. Whisk constantly for 4 minutes.
- Remove from heat. Using whisk attachment, whisk on high for 5 minutes.
- Turn speed to medium. Slowly add chunks of soft butter.
- Add vanilla. Whip for 2 minutes. Scrape bowl.
- Add heavy cream. Whip for 2 minutes.