Step 1

In a medium saucepan, warm the chocolate, water, and butter over low heat, stirring, until melted and smooth.

Step 2

Remove from heat, add the sugar, and let cool to room temperature. Stir in egg yolks and beat a few moments until smooth and creamy, about 5 to 10 seconds.

Step 3

In a separate bowl, beat the egg whites until they form soft peaks, but aren't too stiff or dry. Fold one-third of the egg whites into the chocolate mixture until almost smooth, then fold in the rest. (If the chocolate mixture has gotten too thick, you can rewarm the mixture slightly over a pot of barely simmering water or just over the very low flame on the stovetop if the outside of the mixing bowl is heatproof.)

Step 4

Moisten well a muslin cloth or a clean (lint free) tea towel, and line a 8-inch (23 cm) round glass or earthenware baking dish such as a pie plate, with it, letting the sides overhang the edges over the dish. (You can use a 9-inch/23cm pan or plate, which will result in a slightly lower cake.)

Step 5

Scrape the batter into the dish and smooth the top. Lift the sides of the damp cloth and fold it over the batter, enveloping it.

Step 6

Let chill for 1- 2 days before serving.