HEAT oven to 225°F. BEAT egg whites and cream of tartar in mixer bowl with whisk attachment on high speed until foamy. While beating constantly, ADD sugar, 2 Tbsp. at a time, beating after each addition until sugar is dissolved before adding the next. (RUB a bit of meringue between thumb and forefinger; it should feel completely smooth.) CONTINUE beating until whites are glossy and stand in stiff peaks. BEAT in vanilla.
SPREAD meringue on bottom and sides of greased 9-inch pie plate with back of spoon, building up edge to form a rim.
BAKE in 225°F oven until firm and wooden pick inserted in center comes out clean, 1 to 1 1/2 hours. TURN off oven. LET dry in oven, with door closed, until cool and crisp, at least 1 hour. STORE in pie plate in tightly sealed container at room temperature. FILL just before serving.
For individual meringue tart shells: Line 2 baking sheets with aluminum foil or parchment paper. Using about 1/3 cup for each shell, spoon meringue onto sheets. Use back of spoon to build up edges to form rims. (Baking sheets can be lightly greased and floured; meringue can be piped from pastry bag.)
Chewier texture: This recipe produces a crisp white meringue. If you prefer a more chewy inner texture, reduce baking time to about 40 minutes. Turn oven off and let meringue cool with the door closed.
Lightly browned: If you prefer your meringue with some color, increase the oven temperature to 250°F and bake for 50 minutes. Turn oven off and let meringue cool with the door closed.
Angel pies consist of a crisp meringue shell and a creamy filling. The classic filling is lemon or lime, but any cooked custard, ice cream or whipped cream mixed with fresh fruit will work.