In the world of flourless chocolate cakes there are those who love the dense, cakey intense varieties. Then there is the other world of custardy, rich and creamy versions. And finally, the dry and airy cakes. I've made and eaten all of them, and the ingredients are less important than the technique.
My favorite, by far, is the custardy version which relies on minimal whipping and minimal cooking. The other two varieties leave my mouth feeling like I said something dirty and it was just washed out by a disapproving mother. So in my quest for the perfect recipe I've found a leading contender courtesy of Paul Raphael at Underbelly. His recipe is aptly titled, but slightly modified to add Kahlua:
Intense Flourless Chocolate Cake 4 oz (113 g) 75% Chocolate* 2 oz (57 g) 60% Chocolate* 4 oz (114 b) Unsalted butter, cubed 2 Whole eggs 2 Yolks 1/4 C. Kahlua 2 T. & 2 t. (32 g) Sugar 1/8 t. (.5 g) Salt
*Paul recommends Valrhona Guanaja and Manjari chocolates - which I highly recommend as well. I used El Rey and Callebaut because they were handy.
Oven to 400 F with rack on bottom rung. Butter and dust with cocoa a 6" springform pan, line the bottom with parchment paper and butter. Set the pan on a large double sheet of foil and pull the foil around the sides of the pan and make sure that the whole pan is well wrapped up the sides.
Make double boiler and melt chocolate over gentle heat. Once melted, remove from heat, add butter little by little, stirring gently until melted. Let chocolate cool a bit.
In mixing bowl whisk eggs and yolks just until combined. Remember, you don't want to overwhip this version of cake. Add the sugar and salt and continue whipping. Finally, add the Kahlua. Now, whisk until the sugar dissolves and a light froth forms. Do not create volume!
Gently stir the egg mixture into the chocolate - not the other way around! Once combined pour the batter into the springform filling only to about half way. Put springform into large roasting pan, and pour water to go half way up the side of the springform. Bake about 20 minutes or until there is a slight jiggle left in the center of the cake. If there's no jiggle, you went too far and you just made a dry dense cake. Cool to room temp and plate.