Put the sugar for the caramel and caramelize it. Pour the caramel into a cake form and cover its walls and bottom with it.
Beat the sugar with the eggs, vanilla and gradually pour in the cool milk. Pour this mixture over the caramel and place the biscotti on top. Even if they dry out during baking, once you invert the ready cake, they'll get syruped.
Bake in a water bath in a preheated 320°F (160 °C) oven for about 60 min. Take it out of the oven, wait for it to cool and invert onto a plate. When serving, pour the caramel topping over it.