Melt chocolate and butter together, over a double boiler (or take a pan of boiling water and place a bowl on top to melt them in together and some might like to use a microwave).
After they have both melted, take off the heat and add 2 tablespoons sugar, beaten egg yolks, and vanilla. Mix well.
In a separate bowl beat egg whites and salt until soft peaks form. Add 2 tablespoons of sugar, beat about 2 minutes longer.
Fold in the egg whites into the chocolate until just combined.
Grease 4 ramekins (6 ounces) and place on baking sheet.
Divide batter between the ramekins and bake for about 22-25 minutes.