• Sieve the flour and cocoa together and put them aside.
• Separate the yolks from the egg whites, keep the egg whites aside.
• Pour the yolks at room temperature into the mixer bowl with a whisk hook and operate it at medium-high speed, adding the sugar little by little.
• After about 5-6 minutes the mixture will become clear and frothy, then add the cold water, vanilla seeds, and salt.
• At this point also pour the warm melted butter and mix again for a few moments, then lower the speed to the minimum and add a spoonful of flour and cocoa which were previously sieved together.
• After incorporating the powders, add the heated milk, which should be heated at 40C.

Beat the egg whites with the electric whisk in a separate bowl, adding the lemon juice:

• the egg whites must be semi-whipped.
• Pour the beaten egg whites into the bowl with the cocoa mixture.
• Incorporate the egg whites evenly with a spatula.
• The final compound will be very fluid, almost liquid.
• Pour the dough into the previously lined baking pan (9x9 inches) and bake in a preheated static oven at 150 °C (300°F) for about 70-80 minutes.
• Check the consistency with a toothpick to make sure that it’s still not liquidy.
• Remove the cake from the oven and let it cool completely.
• Put it in the fridge for at least 2 hours.
• Remove the mold and cut it into cubes and sprinkle with icing sugar.