I think you could very comfortably halve this recipe; six young men bent on Dungeoning and Dragoning managed to eat only half, and eight adults had seconds and thirds and left something like two thirds of the cake. (I made a practice cake and a final cake. I am a paranoid baker.) It's a lot of cake.
(If you do halve the recipe, use a 6 inch springform. Reduce the baking time to 16 minutes.)
It's also basically the Ultimate Chocolate Cake over at cook's. It's not remotely good for you. It's really really rich. It's quite tasty.
Preheat the oven to 325 degrees. Warm 8 eggs to room temperature. Grease the sides of a 9 inch springform pan. Cut a circle of parchment paper to fit in the bottom.
Melt one pound of 70% dark chocolate and 1/2 pound of unsalted butter. (I made this with Trader Joe's groceries and I made it with Green and Black's, Strauss butter and cream, and eggs from chickens that allegedly live better than I do. The latter cake was immeasurably better. Sorry.) Break or cut the chocolate and butter into 1 inch pieces, put in a microwave safe bowl, and microwave in 30 second bursts. Stir briefly between each burst. (Yes, you can do this in a double boiler. My mother swears by them. I always burn the chocolate. Sadness ensues.)
At the same time, break all of those freaking eggs into a bowl, and whip (hopefully with a machine) for five minutes, until doubled in volume. This means that one either has a standing mixer, or one does a lot of dancing and utensil switching. It kinda sucks.
When the chocolate is fully melted, give them one more burst of microwaves for good measure. Add 1/4 cup espresso or orange liqueur. (Or nothing.) Whisk melted chocolate and melted butter until they are completely combined. Add the whipped eggs in thirds, mixing throughly between each addition. Pour into springform pan and bang against a counter to smooth the top. Bake in preheated oven for 24 minutes. It won't look done- not even close to done- but look for the crackly surface you get on top of brownies. Let cool to room temperature, and then refrigerate overnight, covered.
Unmold a few hours before serving. (Or one hour.) The edges will need to be freed with a knife. The cake will need to be flipped over to remove the parchment paper and then flipped back. Center the cake on a nice plate and make ganache.
Melt 4 oz. chocolate and add 1/2 cup heavy cream. Mix throughly, perhaps with a dash of the flavoring in the cake. Spread on the surface of the cake quickly and let set.
Just before serving, sprinkle cake lightly with kosher salt. Slice into very thin pieces and eat.