For a (mostly) mess-free option, weigh your egg whites instead of trying to measure them in cups.
Ingredients
1¼ cups egg whites (~300g, ~10 eggs)
2.5 cups sugar
Tools:
Hand Mixer
Steel Bowl
Saucepan
Digital Scale
Directions
Place egg whites and sugar in a very clean stainless-steel bowl and whisk thoroughly till smooth.
Set over a simmering saucepan of water on the stove that is wide enough where the bowl is not touching the water. Allow sugar to dissolve, until it is warm and no longer granular.
Pour into a mixing bowl and whip on high speed with a hand or stand mixer for 5 minutes or until stiff peaks have formed.