French meringue contains only 4 ingredients: egg whites, sugar, salt, and cream of tartar. Continue clicking through this slideshow to learn the proper technique for making French meringue.
Clean and complete separation is critical for obtaining volume when whipping egg whites for meringue. The slightest trace of fat (which the yolks contain) will cause the meringue to be flat and useless. To be sure that you won't ruin an entire batch, separate the whites from the yolks one at a time in a separate bowl, then add them to the mixing bowl after each separation. This way, if you break one, you have only wasted one egg (but go ahead and have it for breakfast instead!)
Begin whipping the egg whites in a stand mixer fitted with a whisk attachment on low speed. As the whites start to look wet and frothy, after about 45 seconds, add cream of tartar and salt and allow it to dissolve with the mixer still on low speed, about 10 seconds.
While the whites are still frothy, slowly begin to add the sugar in a steady stream with the mixer on low. Once you've added about 1/4 cup of the sugar, increase the speed to medium and continue to gradually add the sugar as the mixer runs.
Once all of the sugar has been added, increase mixer speed to high and whip for approximately 4 minutes, until the meringue has doubled in volume and is thick and glossy.
Different recipes will call for either soft peaks or firm peaks. Once the meringue looks big, glossy, and thick, stop the mixer and check to see if the meringue is at soft peak stage by dipping the whisk vertically into the bowl and pulling it up straight, then flipping it over. A "soft peak" will begin to slowly slump over while a firm peak will not move. If you are whipping to soft peaks, the meringue will begin to droop over a bit after being held sideways for five seconds. For firm peaks, the meringue should not move during this test. If the meringue has not reached the desired consistency, continue whipping at high speed for another 30 seconds to 1 minute, then stop and test again.