Preheat oven to 400°.  Separate the eggs.  Crack shell, keeping yolk in one half, white in other. Turn yolk from one half into the other, letting white run into a small bowl, yolk into a medium bowl, preferably with a spout.   Pour each white into large mixing bowl. There can be whites in the yellow, but absolutely no yellow in the whites. Keep whites at room temp to increase air.

Grease the inside of 10 ramekins with butter and sprinkle the sugar inside each to cover the butter.

Make custard.  In medium saucepan with wire whisk, mix flour, cocoa, 3/4 cup sugar, salt.  Gradually blend in the milk. Cook, whisking over medium heat until mixture begins to thicken. Turn heat to low.  Alternate mixing with a rubber spatula and a whisk, until thickened.  Remove from heat.   Beat yolks with the whisk. Pour in about 1/2 cup of the cocoa mixture into the yolks and mix thoroughly.  Gradually whisk the yolk mixture into the saucepan.  Add 2 Tbs butter and the vanilla, stirring until they are combined.  Set aside to cool slightly.  Recipe can be made in advance to this point.

Create air by using an electric mixer to mix the cream of tartar and egg whites.  On high speed, beat just until soft peaks form when beater is slowly raised.  Add 1/4 cup sugar, beating just until stiff peaks form when beater is raised.  Whites will be shiny and satiny.

Fold chocolate mixture into egg whites, by sliding the chocolate mixture into the side of the bowl.  The egg whites will rise up when this is done. With a rubber scraper, gently fold mixture with an under and over motion, turning the bowl 1/4 turns,  just until combined.  Overfolding will reduce the height of the souffles.  Carefully spoon the souffle mixture into the prepared ramekins. Level off the top with the rubber spatula or a butter knife. Bake at 400° for 15 minutes or until puffed and set.

While the souffles are baking, whip the cream. Guests can break top of souffle and insert whipped cream into the center.