Preheat oven to 350 degrees. In a medium sauce pan, melt the butter and chocolate over low heat until smooth. Turn heat off and let cool completely.
While cooling, liberally butter your soufflè dishes. This is important so the cake does not stick!
Use an electric mixer on high to beat the eggs, egg yolks, sugar and salt. Do this for about 5 minutes or until stiff and pale yellow.
Gently fold your cooled chocolate mixture in with the egg mixture until well incorporated. Be careful not to break all the air you created.
Once the chocolate is folded in, sift the flour over the mixture and gently fold that in as well (sifting is just putting your flour through a fine mesh strainer).
Transfer batter to the buttered ramekins or soufflè dishes and place on a baking sheet. Bake for 16 minutes.