Add the sugar, water, and lemon juice to a saucepan on high heat. Do not stir the mixture to prevent crystallization.
When bubbles start to form in the pan start your meringue.
In a grease-free mixing bowl on a mixer fitted with a whisk attachment, add the egg whites, salt, and cream of tartar. Start whipping at high speed until stiff peaks.
In the meantime monitor the syrup. Once it reaches 240 degrees turn off the heat. Lower the speed of the mixer to stir and slowly pour the hot syrup as close to the inside of the bowl as possible to avoid splashing.
Once all of the syrup is added, increase the speed to high. Continue whipping until the bowl is cool to the touch, then add the vanilla extract.