In a small saucepan fitted with a candy thermometer, bring the water, corn syrup and 3/4 cup sugar to 246 degrees.
In the meantime, in a completely clean, dry mixing bowl, with and electric mixer, whisk the egg whites, salt and cream of tartar until creamy and foamy, about 2 minutes. Still whisking, sprinkle in the remaining 1 tablespoon of sugar and continue to whisk until the whites hold very soft peaks, about 2 minutes. While mixing on slow speed, carefully drizzle in the hot syrup. Turn the mixer to high and whisk until thick, fluffy and just warm, about 7 minutes. Turn the mixer to low and whisk in the vanilla.