Custard: Whisk together the egg yolks and sugar until completely combined. Add flour, whisk very well and set aside while heating the milk. Heat milk, heavy cream, butter and salt until simmering. Slowly add the heated milk mixture into the egg yolk mixture stirring constantly. Whisk well, slowly. Return the mixture into the pot and bring to simmer stirring constantly. The mixture will thicken within 30-45 seconds. Take off heat! Whisk in the vanilla, set aside to cool to room temperature.
Crepes: Preheat a non-stick pan on medium high heat. Combine flour, eggs, milk, oil, salt, sugar and baking soda. Whisk all well. Slowly, start adding 1/4 cup of the hot water at a time to the batter. Whisking constantly until the batter reaches the consistency of melted ice cream. Pour about a ladle-full into the hot pan and swirl slowly. For this cake, I used a little bit more batter on each crepe and spread around to about 8-inch round crepe. (Normally, I use 1/2 ladle-full.) Cook for a few seconds on each side, until golden.
Ganache: Bring the heavy cream to boil, be careful not to let it actually boil or it will raise.
Pour the boiling cream over the chopped chocolate and stir until melted. Cool to a little warmer then room temperature.
To assemble the cake: Spread a somewhat thin layer of custard on each crepe as you stack them of top of each other. Pour the ganache over the top of the cake. Refrigerate for a few hours or overnight to let the cake set.
Ganache can also be poured on the cold cake, before serving.
(*Suggestion:* if you want extra security to keep the cake from sliding off while it's chilling, use one of those long, wooden kebab sticks in the center of the cake.)