In a saucepan, heat water, sugar and corn syrup over medium heat. Whisk occasionally. Heat mixture until candy thermometer reaches 240 degrees.
While the sugar mixture is heating, beat egg whites and cream of tartar in stand mixer with the whisk attachment. Beat on medium-high until soft peaks form (about 2 minutes).
When the sugar mixture reaches 240 degrees, remove from heat.
With your mixer on low, slowly add sugar mixture to the egg whites.
Once all of the sugar mixture is added, turn the mixer to medium-high and whip until stiff peaks form, about 7-9 minutes.
Stir in vanilla during last minute of whipping. Mixture will be thick and glossy white.
Store in air tight container for up to two weeks.
Notes
Making your own marshmallow creme is easy and extremely frugal! It is definitely worth making your own.