Put the water, milk, salt and butter in a suitable container. Turn the stove on and once the mixture comes to a boil, pour in the flour, while stirring vigorously until the mixture clumps up and you get a smooth steamed dough. Leave the dough to cool.
To the cooled dough, add the eggs, 1 by 1, while stirring until the dough absorbs them.
Divide the mixture into 2. Cover the bottom of a form with a cake ring with baking paper. Pour in one part of the dough and spread it out along the entire bottom, without evening it out. Bake in a preheated oven until golden. Do the same for the 2nd layer.
Make a cream by beating the eggs with the sugar, then add the starch, stirred in 2/3 cup (150 ml) milk. Add the mixture to the rest of the warm milk (pot on low heat) and stir nonstop until you obtain a fluffy cream. Add the vanilla.
Leave the resulting cream to cool.
Beat the butter to a fluffy cream. Add it, spoon by spoon, to the other cooled cream and stir with a mixer until the mixture becomes homogeneous.
Pour cream over the 1st layer you made, smooth it out evenly and place the 2nd layer on top.
Leave it to set for about 2-3 hours. Sprinkle the ready cake with powdered sugar.