Dissolve the fresh brewer’s yeast in 50 g of warm water, then knead it with 100 g of flour. Shape it into a ball and leave it to rise in a covered bowl in a warm place, for about two hours.
Emulsify the olive oil with the soft butter, the orange zest and the vanilla seeds, then scrape it into a bowl. Add the egg, the egg yolks, the sugar, the orange juice and a pinch of salt and whisk until smooth.
When the first dough has doubled, add the olive oil, butter and egg mixture and start kneading, adding little by little the rest of the flour. You will get a smooth, soft and very elastic dough.
Scrape it into a 30 cm x 22 cm rectangular pan and smooth the surface. It must have a 2 cm thickness.
Leave it to raise, loosely covered, in a warm place for about 3 hours.
When doubled, bake in a hot oven at 180°C for about 30 minutes. It will be ready when it will be hazel brown, soft and when a toothpick inserted in the centre will come out clean. Let it cool on a wire rack.
While the schiacciata is cooling down, make the chantilly. Heat the milk with the vanilla pod. Bring it to a soft boiling, then turn off the heat and set it aside.
In a saucepan whisk the eggs with sugar and corn starch, removing all the lumps. Pour the milk into the eggs in a thin stream, stirring constantly not to cook the eggs.
Return the saucepan over the stove and cook the custard over low heat, stirring with a whisk, until thick. Remove from the heat as soon as it starts bubbling. Transfer the custard into a bowl, cover it with cling film and let it cool down completely. To speed up the cooling process, immerse the custard bowl into a larger bowl with iced water.
Whip the cream to soft peaks and gently fold it into the cold custard.
Slice the schiacciata in half, fill it with the chantilly and sandwich it again, then dust with icing sugar. You can decorate the schiacciata Fiorentina with cocoa powder to reproduce the Florentine lily. Let it rest in the fridge for 30 minutes before serving.