Mix the room temperature butter and sugar well with a whisk.

Whisk egg white until it becomes white. Add it to step 1 littler at a time and mix well between each additions.

Pour the dough in a butter coated cake pan. Tap the bottom and eliminate air pockets.

Bake in a 170℃ preheated oven for about 30 minutes. Stick a toothpick through the cake and when nothing sticks to it, then it is ready.

Make the creamy chocolate while letting step 5 cool. Chop up the chocolate bars. Heat up heavy cream until it is right about to boil. Then stop the fire, add the chocolate and melt it.

When step 5 becomes cool enough that you can touch it with your hands, cut off the broken part and cut the rest into 2 pieces.

Put back the part which would be the bottom back in the cake pan. Pour the creamy chocolate from step 6 and place the other half of cake on. Cover with a cellophane wrap and let it chill in the refrigerator.

Turn the cake pan over a cake cooler. I don't have a cake cooler, so I use grill + shallow container for this, and take the cake out. It would be easier to take the cake out if you warm up the sides.

Melt the confectionery chocolate over hot water. Pour it over the cake and coat it.

Let it chill to harden again....and it is ready ! You can also decorate it like this using a chocolate decorating pen.