Mix a small amount of the cold water with the smaller portion of corn starch. Set aside.
Heat the rest of the water to 185/195°F (85/90°C).
Pour some of the hot water over the cold water and starch mixture. Put everything back in the pan and bring to a boil.
Gradually pour into the unmelted chocolate, whisking all the while to emulsify. Add the egg yolks, mix, then add the larger amount of starch and mix.
Whip the egg whites with all the sugar until soft peaks form.
When the ganache has reached 95/115°F (35/45°C), gently fold in the egg whites using a spatula.