1. Melt dark chocolate, butter, salt in the microwave in 15-20 second intervals until fully combined and melted.
2. Let cool.
3. Mix liquid egg whites in a stand mixer or electric hand mixer until foamy - slowly add sugar and then mix on high until stiff peaks.
4. Add egg yolks to the chocolate mixture.
5. Add in 1/3 of the egg white mixture to the chocolate mixture so it's easier to fold the rest of the egg white mixture. Once it's combined, add in the rest of the egg white mixture and fold gently to combine everything.
6. Preheat oven to 400°F.
7. Butter 4 ramekins and dust with granulated sugar, bake for 15 minutes (do not open the oven before the timer goes off, or else the soufflés will deflate!) Make sure soufflés are not jiggly in the middle.
8. Add powdered sugar on top and eat within 90 minutes!

Recipe Notes: Liquid egg white might take a long time to get stiff - if it doesn't end up getting stiff, still add it in chocolate mixture and it'll still bake well!