Beat the eggs in a bowl. In another bowl, pour in the condensed milk, water and vanilla. Stir and pour it into the eggs.
In another container, pour in 1 tsp lemon juice, 1 tsp water and 1/5 cup (70 g) sugar. Put it on the stove and caramelize.
Pour this caramel over the bottom and sides of a small rectangular form. Peel the apples and cut them into thin slices. Arrange a layer of apples over the caramel and a layer of biscotti on top.
Alternate in this order until out of ingredients. Pour the egg mixture on top and wait for the biscotti to absorb the liquid. Bake the cake in a water bath in a preheated 320°F (160 °C) oven for 1 hour.
Wait for it to cool and invert onto a plate. Pour on the caramel topping and put it in the fridge for 2 hours.