Technical Stages :

• Sourdough :
• Dilute 1/4 of the flour with the yeast in some lukewarm water.
• Make a soft ball.
• Let it double in volume in a warm place.
• Dough :
• Put the remaining flour in a fountain shape, and add the eggs, salt and sugar. Knead with the tip of yoru finger with a bit of cold water to get a flexible, nonsoft dough.
• Add the sourdough, knead, tear to mix well. Add the soft butter, knead again. Put in a covered ball in a temperate location. As soon as its volume doubled, tear the dough, and repeat 15 minutes later. Put it then in the fridge for 30 to 40 minutes, or even for a few hours, tearing it every time it rounds up.
• Shape it into a ball, and stretch on a buttered baking sheet into a round wafer 25 cm (9,84 inches) in diameter.
• Let it rise for 45 minutes in the fridge.
• Glaze with beaten egg yolk, sprinkle with coarsely ground sugar chunks. Bake in warm oven at 240°C or 464°F. As soon as it starts to get colored, turn the heat down to 200°C or 392°F. Bake for 25 minutes. Check if it is baked. Let it cool. Cut two layers.
• Cream :
• Put the water and sugar in a small pot, the 3 egg yolks in a larger one. Boil the sugar for 2 to 3 minutes. Pour it gently on the beaten egg yolks, whisking over low heat.
• Keep on whisking firmly for 2 minutes, take away from the stove and whisk until fully cooled.
• Whisk the chantilly with the vanillated sugar, add the yolks, whisk until the cream stays in the wires of the whisk.
• Spread on the biscuit and cover with the other half.
• Keep refrigerated.