Start with preparing the Crème Patisserie, as it will need to be completely chilled.

In a medium heavy-bottomed saucepan add the milk, the grated zest and the vanilla extract, put it on a medium to low heat on the hob and bring very gently to a simmer.

In the meantime, in a bowl add the egg and the caster sugar. Beat with a whisk until you get a creamy pale mixture.
Now add the flour and continue to whisk until you don't have any more lumps.
At this stage, if the milk is starting to simmer, remove it from the heat and pour it into the egg mixture whisking continuously and mixing well.
Pour the mixture back in the pan and place it on a medium to low heat.
It is very important that you stir the mixture with a whisk all the time to prevent it from sticking to the bottom of the pan and from forming any lumps.
The Crème Patisserie will start to thicken but you will need to carry on whisking for about 3 minutes to cook the flour.
Now remove it from the hob, place some cling film directly on the top of the Crème and let it cool completely. To speed this step, place the pan into the kitchen sink filled with cold or iced water.

In the meantime, wash and thoroughly dry the raspberries and set aside.
Crumble the biscuits and set aside. In a clean bowl, place the cream and add the icing sugar. With an electric hand whisk, whip the cream until it forms soft peaks.
If the Crème Patisserie has now cooled down, transfer it into a clean bowl and start to add the whipped cream into the Crème a little at a time, folding in with a spatula or a spoon from the bottom to the top.

Now you can start to assemble the dessert - building in two layers. At the bottom of the dessert bowl, place half of the crumbled biscuits, spoon the Crème Diplomate on the top and arrange some of the raspberries. To finish it off, grate some chocolate on the top.
Repeat in the other bowl.
Place the bowls in the fridge at least 1 or 2 hours before serving.

Start with preparing the tart case: lightly smear with butter then scatter with flour, shake to distribute and discard the excess.

Now prepare the pastry:
If you have a freestanding mixer, put the flour, sugar and butter into the mixer bowl, with the paddle attachment, mix together at a medium speed, until it becomes a crumble.
Then add the egg, the egg yolk, the lemon zest and set the mixer at low speed and mix until it starts to form a ball; if the dough is still too wet, add one tablespoon of flour at a time, to a maximum of three.
Remove the dough from the bowl and on a lightly dusted surface, roll it into a squash ball, wrap it in cling film and put it in the fridge for about 20-30 minutes.

Whilst the pastry is chilling, pre-heat the oven to 170°C/180°C and start to prepare the filling.
In a clean bowl, whisk the egg white with an electric hand whisk until it forms soft peaks and set aside.
Remember that the egg should be at room temperature. In another bowl, put the ricotta, the sugar and the egg yolk, mix everything well until you have a creamy mixture.
Now add the chocolate chips, the sherry and mix again.
Now incorporate the egg white a little at a time, folding in with a spatula or a spoon from the bottom to the top.

Take the pastry out of the fridge. Cut it into two parts, one bigger than the other, about ¾ and ¼.
On a lightly dusted surface, roll out the bigger part into a round shape, big enough to line the prepared tart case, including the border.
Pour the mixture into the lined case and roll out the rest of the pastry, cut 7 or 8 strips about 20cm long and 1 cm wide. Place the cross-linked strips on the top of the tart in other words, as a lattice and bake it for about 30 to 40 minutes, until golden brown.

The ricotta tart can be kept in the fridge for 3 days, covered with cling film or aluminium foil.