Melt butter in sauce pot and then add flour.
Cook over medium heat for about 3 to 4 minutes.
Add the milk while whisking and return to a full boil then reduce to simmer for about 5 minutes and add chocolate.
Remove from heat and whisk in Vanilla.
With a mixer beat the yolks until light and pale yellow then fold into chocolate mixture.
In a clean bowl and beaters whip whites to soft peak stage. About 5 minutes.
Fold the whites with the chocolate mixture and fill a large soufflé dish that has been buttered and sugared.
Bake at 375 degrees for about 25 minutes until the top crowns evenly over the dish. Serve with hard sauce or crème anglais (Melt vanilla ice cream)