Mince the chocolate bar and melt together with the butter by immersing in 70-80°C hot water bath (if this is too much trouble, you could microwave it).

Use a whisk to beat 3 egg yolks for 2 minutes (it should start to become white). Once beaten and slightly warm, add to the mixture in Step 1 and mix.

Whisk 3 egg whites. Once stiffened, add the sugar in 2 to 3 portions and mix. Continue mixing until the meringue forms peaks.

Add a third of the meringue to the chocolate bowl from Step 2 and mix. Lightly combine the rest of the meringue. Try to leave the delicate bubbles as intact as possible.

Lightly mix in the sifted dry ingredients. Pour into a baking-sheet lined pan and bake in the oven at 160°C for 45 minutes.

This is what it looks like after baking. Once it's cooled, remove it from the pan and refrigerate. After half a day, it'll deflate.

Bonus: For the baking sheet, cut into a large circle and insert cuts into the high parts. Apply margarine to secure the paper on the pan.