Preheat the oven to 300 degrees F (150 degrees C).

In a large bowl, beat egg whites, cream of tartar, and salt until soft peaks form. Add vanilla; slowly beat in sugar until very stiff and glossy. Spread meringue mixture into a 9-inch pie plate to form a shell.

Bake in the preheated oven for 50 minutes. Turn the oven off; leave meringue in oven for 1 hour. Let cool.