Gateau au chocolat - The best chocolate cake

My mum used to make this cake all the time. It's simple and delicious. 

Ingredients

For the cake:

1 glass of milk (or roughly 100 ml)

125 dark chocolate, chopped roughly

75g butter, chopped roughly

25g sugar

1 packet of vanilla sugar

75g flour

3 eggs, separated

And the ganache:

125g dark chocolate

Double cream / crème fraiche (at least a big, heaped tablespoon. We're not counting the calories, here.)

Method

Melt the chocolate and milk together over low heat, without boiling.

When the mixture has turned into a smooth cream, add the butter, sugar, flour and vanilla sugar. Stir well.

Remove from the heat and add the egg yolks, one by one. Mix well in between.

In another bowl, whip the egg whites with a pinch of salt, until stiff. Gradually and carefully add it to the chocolate mixture. Don't overmix it: the air from the egg white is what will make the batter rise when cooking.

Pour in a buttered and floured round cake tin and cook in a preheated over at 200 degrees, for 30 minutes or so. I usually check after only 20 minutes if it's cooked already. The blade of a knife should come out clean, and the top of the cake should not be crispy.

Once cooked, take out of the oven and put a cloth (e.g. kitchen towel) on it, to stop it from drying.

While it's cooling down, make the ganache by melting the chocolate and cream together. It's OK if the mixture is a bit grainy, this is not a Michelin restaurant cake :) 

Remove the cake from the tin, then add the ganache on top and all around it.

It's best kept in the fridge but served at room temperature. The ganache should be thick yet soft. If it stays hard, it means there is not enough cream with the chocolate.