Bring all ingredients to room temperature.
Make the espresso and poor it into shallow flat-bottomed bowl. Add one shot of cognac, one teaspoon cocoa, and allow to cool to room temperature.
If at this point you've decided to use coffee instead of espresso, take the coffee you've made and drink it. Then make espresso. Separate egg yolks and whites.
In the first mixing bowl, beat egg yolks and sugar until creamy white. Add mascarpone and 1 shot of cognac and mix until blended. Leave this mixture in the bowl.
In the second mixing bowl, beat eggs whites until fluffy. If you use pasteurized eggs, this may take a while.
Fold beaten egg whites into mascarpone mixture. Mix only enough to blend. Over mixing will deflate the egg whites.
Quickly dip a savoiardi in the espresso bowl. To get the right amount of espresso on the savoiardi, lay the finger flat in the bottom of the bowl sugared side UP and immediately pull it out. Place each finger flat in the bottom of the pan sugar side DOWN. The savoiardi will quickly absorb the espresso. If you soak the savoiardi in the espresso you will end up with soggy savoiardi instead of moist savoiardi.
Build a layer of dipped savoiardi across the bottom of the pan. If some of the savoiardi do not look 'dark' from the espresso, spoon a few more drops of espresso on the savoiardi. Any espresso left in the bottom of the pan will be absorbed by the savoiardi. Too much espresso will turn the fingers into a soggy mess.
Spoon a layer of egg/mascarpone mixture across the layer of savoiardi. Use about 1/2 of the mascarpone mix. The layer should be about 1cm. (3/8in.) thick.
Dip another layer of savoiardi and lay them on the mascarpone mix. Layer them as before, sugar side down. Drip espresso on the savoiardi that don't look dark from the coffee.
Spoon a second layer of egg/mascarpone mixture across the second layer of savoiardi. Use the remaining mascarpone mix. The layer should be about 1cm. (3/8in.) thick.
Sift cocoa on top of the second mascarpone layer. Scoop a tablespoon of cocoa into a small sieve. Hold the sieve over the tiramisu and tap the sieve on the side with your finger. The cocoa should sprinkle down in an even layer. Use this technique to cover the tiramisu with a very thin layer of cocoa.
Refrigerate for at least 4 hours before serving. The Tiramisu will taste quite good for several days if refrigerated.