Fold a kitchen towel and set in the bottom of a large skillet. Fill with water and bring to a gentle simmer over medium heat.
Place the chocolate in a small heatproof bowl. Set in the pan of simmering water and stir until the chocolate is completely melted, 3-5 minutes. Carefully remove the bowl from the water and set aside.
Combine the egg whites and 1 tablespoon of sugar in a medium heatproof bowl. Set in the pan of simmering water and stir until the mixture reaches 140˚F (60˚C). Carefully remove the bowl from the water.
Using an electric hand mixer, beat the egg white mixture until soft peaks form. Set aside.
Set a medium heatproof bowl in the pan of simmering water. In the bowl, combine the egg yolks, water, and remaining tablespoon of sugar. Beat with an electric hand mixer until foamy and the temperature reaches 160-170˚F (70-75˚C). Carefully remove the bowl from the water.
Add the melted chocolate to the yolk mixture and mix with a rubber spatula until well combined.
Add a scoop of the egg white mixture and stir to combine. Add rest of the egg white mixture and fold to incorporate.
Divide the mixture between 4 serving cups. Chill in the refrigerator for at least 1 hour, or until set.
Top with whipped cream and cocoa powder, if desired.