A metal bowl is best for cooked meringue so that the heat of the water is transferred quickly. The meringue can be whisked by hand with a balloon whisk, or with a hand-held electric beater.
Put the egg whites, sugar and vanilla in the bowl and whisk with a balloon whisk or electric whisk until they are well mixed.
Set the bowl over a pan of simmering water and whisk until the mixture forms a stiff peak when the whisk is lifted, 10-15 minutes. Take from the heat and continue whisking until the meringue is cool.