In a microwave-safe bowl, melt the chocolate. Add and thoroughly whisk together the eggs, sugar, and flour.
Pass the mixture through a strainer to remove any lumps and to filter out the chalazaes (the little white strands that attach the yolk to the egg white). Transfer to whipper and pressurize.
Spray mixture into a greased glass, ramekin, or whatever microwave-safe container you will cook it in, leaving at least the top third of the container empty. (A clear glass is nice to use, as you can can see the cake rise and fall as it cooks.)
Microwave for 30 seconds or until the foam has set.
Flip onto a plate and dust with powdered sugar.
(For better-tasting results, try adding Nutella or Fluff: Spray a thin layer of cake batter, drop a spoonful of filling into the center, and then spray more cake batter on top of and around the filling.)