In a saucepan boil the water with the butter (oil) and salt.

When boiling add the flour at once and remove from heat mixing well until flour is all incorporated.

Return to medium heat 1-2 minutes, stirring continuously, until the dough starts to stick to the bottom a little.

Remove from heat again and leave to cool until just slightly warm.

Add the eggs to the dough one by one, and mix well after adding every egg, until the egg is fully incorporated.

On two parchment papers, draw on each a circle with approximately 24-26 cm diameter, and distribute the dough between those two circles, spreading it uniformly and thinly. I leave a finger between the dough and the circle, in the oven it will expand a lot, more than the circle. So keep that in mind.

Bake the circles on the back of a baking tray, in a preheated oven at 220°C for 10 min, then lower the heat to 180°C and bake them 20 min more.

Remove from the oven and completely cool on a cooling rack.

While the circles bake, prepare the filling by mixing the milk, eggs, sugar, vanilla and corn starch. I start with just a little milk and the rest of ingredients until they are completely mixed, and then I add the rest.

Cook the filling on a medium heat, stirring continuously, until it thickens.

Remove from the heat and add the butter in the hot mixture, stirring very well until the mixture is smooth.

Leave it to cool (covered) or cool it on a water bath.

Lay one of the circles on a serving plate, add the cooled filling, layer the other circle on top and press slightly.

For the ganache, chop the chocolate, heat the whipping cream until it starts to boil, and add it to the chocolate.

Stir patiently until smooth and pour on top of the cake.

Leave for at least two hours in the fridge and then serve.