Here's a simple recipe for Swiss Meringue, perfect for making frosting or pies. Ideally, you'll have a thermometer to measure the temperature of the mixture precisely. Make sure to use a clean bowl that fits just snugly over the pot without touching the water.
Place the egg whites and sugar in a mixing bowl placed over simmering water. Stir continuously until the mixture reaches 140 degrees, or until the sugar has completely dissolved. Transfer to the bowl of an electric mixer and begin to whip on medium-high speed. Continue to whip until the mixer bowl is cool to the touch.