Put the raisins in a bowl, cover them with boiling water and, if desired, 1 tablespoon of dark rum. Leave them like this for about 30 minutes, then drain the raisins in a mesh strainer, so that it loses the water.
Make the cornerstones of French pastry: the crème pâtissière. Heat the milk with the vanilla pod, bringing it up to the boiling point and then turning off immediately. Whisk the egg yolks and sugar with a fork in a bowl heat resistant, then add the flour and mix again, until you get a smooth, dense and homogeneous mixture.
Start diluting it with 2 - 3 tablespoons of warm milk, then remove the vanilla pod and pour the milk into the bowl, stirring with a hand whisk.
Put everything back into the pot where you heated the milk, place it over a medium heat and cook, stirring slowly and continuously, for about 5 minutes, until you get a thick, soft and homogeneous cream, very fragrant.
Cover the cream with cling wrap by touching the surface of the cream to avoid any crust from forming, and let it cool down.
Take the puff pastry out of the refrigerator and put it on a work surface lightly floured if needed. Prepare a baking sheet lined with parchment paper.
Roll out the dough into a rectangle of about 25 × 40 cm. Spread the cold cream over it, leaving the edges free. Sprinkle the raisins on the surface, then roll the dough on itself, so as to obtain a compact cylinder of about 25 cm long. Cut 10-12 wheels from the cylinder and arrange them on the baking sheet. Turn on the oven at 180°C (static). Brush the sweets with egg whisked together with the water, then put in the oven and cook for 22 - 25 minutes: they must be golden and crunchy on the surface. Let them cool on a grill and serve them cold. You can keep them 1 day on a tray covered with perfectly adherent food cling wrap.