Oven at 450 degrees Fahrenheit. Butter 4 ramekins.
In a double boiler, over simmering water, melt butter and chocolate whisk until smooth. In a bowl, beat the eggs, egg yolks, sugar and salt at high speed until thickened.
Quickly fold the chocolate mixture into the egg mixture along with the flour. Spoon the batter into 4 prepared ramekins, bake for 12 minutes, or until the sides of the cakes are firm, centers soft. Allow to cool in the ramekins for 1 minute, then invert onto a dessert plate. Carefully turn each one over, let stand for 10 seconds and then unmold. Serve immediately.