Preparation: Line the cake tin with paper, chop the chocolate, leave the butter at room temperature to soften. Mix the plain flour and cocoa powder and then sift.
Put the chopped chocolate in a bowl and put the bowl over a bain-marie to melt the chocolate. Add the cream and stir until smooth. Remove the bowl from the bain-marie and leave to cool.
※Do not let the chocolate cool too much. Otherwise the chocolate will harden and it will be difficult to mix with other ingredients at the next step.
Cream the butter and add the powdered sugar. Whip until fluffy. Add one egg yolk at one time and whisk constantly to incorporate air.
Add the cooled chocolate to Step 3 and whisk.
Make the meringue. Put the egg whites in a bowl and add the sugar in 2 to 3 batches. Whisk until stiff peaks form (until the meringue doesn't drop when you hold the bowl upside-down.)
Scoop 1/4 of the meringue with a spatula and add to the chocolate mixture. Combine gently and lightly.
Add the sifted flour and cocoa powder and stir until everything is mixed well. Add the liquor (or milk) and loosen the batter.
Add the rest of meringue and fold in evenly.
Pour the batter into a cake tin lined with paper and flatten the surface.
Bake in an oven pre-heated to 160°C for about 50 minutes. It'll ready when you insert a skewer in a crack on the cake and it comes out without uncooked batter.
Remove the cake tin from the oven and drop the tin when you hold. Leave to cool the cake in the tin. After it's cooled down remove the cake from the tin and sprinkle with powdered sugar.
If you melt the chocolate and butter at the same time (this is a normal procedure for making a chocolate cake), the cake will shrink a lot and won't look as nice.
With this method the air is incorporated in the cake evenly and you will have a thick cake. On the day you make the cake it is soft and the next day it will be dense and moist. It will be tasty on either day.
This is a rich cake so I made the 18-cm cake less thick, compared to a 15-cm cake. The baking time is the same.
If you like, you can fill the baking tray with some hot water and place the baking tin with the batter on top -- this will make it extra moist and soft. It won't burn easily so it will be nice for those who don't like the slight bitterness of chocolate.
Story Behind this Recipe
I tried a lot of gateau chocolat recipes but sometimes the resultant cakes were dry or too bitter. This recipe gave me a really moist and soft cake, though!
Use your favorite liquor. On the day you bake the cake, the fragrance of the liquor will be on the strong side, so if you'd prefer, you can swap it out for milk instead. If you want to make a thick 18-cm cake increase the quantities to 1.5 times of a 15-cm cake. Adjust the baking time as you see fit.