First of all, prepared the cake batter for the 2 “disks” that form the bottom and top: in a bowl, beat the eggs with the sugar for about 10 minutes, preferably with a hand mixer, until light and frothy. Fold in the two types of flour, sifted together with the baking powder, working delicately from bottom to top to keep the mixture light. Add the butter, melted over a very low heat and cooled down well, and stir until everything is incorporated and the mixture is smooth. Pour half of it into a round springform cake tin (approx. 24 cm in diameter) that is well-greased and dusted with flour, and bake in a preheated oven, at 180 °C, for about 15 minutes. Remove from the oven and leave to cool; then open the tin, remove the disk of cake and lay it on a plate After cleaning the tin, greasing it again and dusting it with flour, pour the other half of the cake batter into it, cook it in the same way as before and leave to cool. If you have 2 identical cake tins, you can obviously bake the 2 cake disks at the same time.
In the meanwhile prepare the filling: peel the pears, remove the cores and cut the fruit into roughly 1 cm cubes. Cook them in a heavy-bottomed frying pan with 50 g of sugar, the knob of butter and the filtered lemon juice. When the pieces of pear have released their juice, add the corn starch dissolved in the Vin Santo; stir, allow to thicken, turn off the heat and set aside to cool. Press the ricotta through a sieve into a bowl and, using a hand mixer, combine it with the remaining sugar and the vanilla seeds (scraped from the pod, cut open lengthwise with a sharp knife). Whip the cream to stiff peaks and mix it with the ricotta; fold it in delicately and, when the mixture is homogeneous, also add the pieces of pear (they need to be cold) and incorporate them carefully.
Place the ring of the springform tin around one of the disks of cake and close it, pour in the filling, level the surface, carefully lay the second disk on top and press down gently with your hands. Put the cake in the freezer for an hour and then in the fridge for at least 6 hours, or better still all night. Before serving, remove the ring of the springform tin, sprinkle with plenty of icing sugar, decorate with the coarsely chopped hazelnuts ... and your beautiful, delicious cake is ready!