This my go-to flourless chocolate cake recipe...and I've tried a few. I think it's the 2 sticks of butter. The bittersweet chocolate I use is the Ghiradelli. I also add a teaspoon of instant espresso to the batter. It deepens the flavor of the chocolate.
Another fantastic recipe from Real Simple. It is easy to make, can be prepared ahead of time, keeps well in fridge (or freezer) and a little slice is perfect. The creme fraiche whipped cream is a delicious addition as are fresh berries.
This is a good recipe, but this recipe would not be good for a Kosher Seder meal, because of the dairy in it.
I've made twice. The second time I substituted 2 Lindt Dark Chocolate Intense Orange bars for the bittersweet chocolate. The small bits of dried orange peels in the bars baked into the cake well. The result was an intensely rich and lovely cake. I will make again with this substitution.