Make sure there are no yolk specks in egg whites and that bowl and beater are immaculately clean and free from grease. Add sugar very slowly, beating well after each addition to dissolve sugar fully. (If not fully dissolved, baked meringue will "weep" with beads of sugar syrup.) Do not overbeat, especially with large electric beater. Meringue should spread smoothly and not lump. Be sure to preheat oven to low (250 degrees).

4 egg whites, at room temperature
1/4 tsp. salt
1/2 tsp. cream of tartar
1 c. sugar, preferably superfine
1/2 tsp. vanilla

Lightly grease 10-inch wide 1 1/2-inch-deep pie plate. Beat egg whites and salt until foamy. Beat in cream of tartar. Continue beating while gradually adding sugar 2 tablespoons at a time, beating well after each addition until sugar dissolves and meringue is very stiff and glossy but not dry. Beat in vanilla. Spread evenly on bottom and sides of plate. Bake until firm and light golden brown.