Lightly butter eight 6-ounce ramekins, and dust them well with granulated sugar. Set them aside
Melt the chocolate in a double boiler, covered, over barely simmering water. Remove the cover, and stir until the chocolate is smooth. Remove the top pan of the double boiler from the heat
In a small saucepan, melt the butter over moderate heat. Stir in the flour and cook until the mixture is thickened but not browned, 1 to 2 minutes. Add the milk, and whisk briskly until mixture is smooth and thick, about 3 minutes
Remove the pan from the heat, add the melted chocolate, and whisk until smooth. Whisk in the egg yolks and vanilla, and set the pan aside
Beat the egg whites and lemon juice at medium speed until soft peaks form, about 1 minute
Gradually sprinkle the granulated sugar on top; continue to beat at high speed until the whites are stiff but not dry
Using a rubber spatula, stir one-quarter of the whites into the chocolate mixture to lighten it, then fold in the remaining whites
Spoon the mixture into the ramekins, filling each to the top. At this point the souffles can be refrigerated, uncovered, for up to 5 hours
Preheat the oven to 375 degrees. Bake the souffles for 17 minutes, or until they are puffed and slightly cracked
Dust them with confectioner's sugar, and serve them immediately. Pass a pitcher of the White Chocolate & Rum Sauce.
