Put chocolate and Cognac into small pan, cover with foil, and set into very hot tap water and heat for a few minutes. Turn off heat and let chocolate soften in the Cognac.
Butter a 6-cup charlotte mold and coat with flour. Hit pan on edge of sink to knock out surplus flour. Preheat oven to425 degrees.
Beat yolks in small mixer bowl until thick and light. Combine cake flour, ¼cup sugar, and salt.
When chocolate has softened, stir into the Cognac and start adding the butter. Stir in a piece at a time, adding the next piece once the previous one has melted into the chocolate. Stir flour-sugar mixture into the chocolate and then add to the yolks. Beat well to mix.
Beat whites until they start to stiffen. Gradually add sugar, then vanilla. Beat until very stiff. Stir about ¼ of the beaten whites into the batter to lighten it and then fold in the rest. Mix well. Pour into prepared pan. Bake 20 minutes, or until cake has risen to the top of the pan and the top begins to crack. Turn off oven and leave cake for 5 minutes. Remove and set on wire rack to cool. Cake will deflate back to its original size. It will be cake on the outside and pudding within.
When dessert is cool, run a knife around the top edge and then to the bottom. Place serving plate over the top and invert. Serve with cream sauce. Make the sauce a day in advance and serve it cold with the kalouga. Crème Chantilly is also good with it.