Immediately make MERINGUE after the filling (such as for Lemon Pie filling is still hot and poured into pie crust).
MERINGUE:
1 Tbls. cornstarch
1/3 cup cold water
5 EGGS WHITES, room temperature
1/4 tsp. cream of tartar
1/2 cup sugar
1/2 tsp. vanilla
DISSOLVE cornstarch in cold water in small saucepan; bring to a boil, stirring constantly.
Remove from heat; cover.
BEAT egg whites and cream of tartar in mixer bowl with whisk attachment on high speed until foamy. Beating constantly, ADD sugar, 1 Tbls. at a time, beating after each addition until sugar is dissolved before adding the next.
Continue beating until whites are glossy and stand in soft peaks. Beating constantly, ADD cornstarch paste, 1 to 2 Tbls. at a time. BEAT in vanilla.
POUR your hot filling (lemon pie) into pie crust. Quickly SPREAD meringue evenly over filling, starting at edge and sealing to the crust all around; swirl with back of spoon.
BAKE in upper third of 325°F oven until lightly browned, 16 to 18 minutes. Cool on wire rack 30 minutes to 1 hour.
Tips:
A hot filling is important. The heat of the filling cooks the bottom of the meringue and prevents it from weeping and creating a slippery layer between filling and topping. Set up your equipment and measure meringue ingredients before you make the filling and work quickly to make meringue before filling cools.
To check if sugar is dissolved: Rub a bit of meringue between thumb and forefinger. If sugar is dissolved, it will feel completely smooth. If it feels grainy, continue beating.
What's a soft peak? To check for soft peaks, stop the mixer and lift the beater. The peaks left in the meringue should curl at the tips. If the peaks stand straight and tall (stiff peaks), the meringue has been over beaten.
Anchor the meringue. Be sure to attach the meringue to the crust all around the edge of the pie. This prevents the meringue from pulling away from the edge during baking.
Beads may form on meringue when refrigerated; gently touch beads with tip of paper towel to absorb.
Refrigerate any leftover pie promptly.