If the ricotta seems to be too wet (it should be firm) before using it, leave it on a sieve for about an hour in order to drain off excess liquid.
In order to turn the ricotta into an even creamier consistency pass it through a fine sieve.
It is a step that I recommend to take with all ricotta based desserts. I’d suggest adding an extra 20 g of ricotta to obtain the required measurement as a small part of it tends to stay clogged in the sieve.
In a large bowl mix very well, until obtaining a creamy consistency, the mascarpone, ricotta, lemon zest and half the amount of sugar. Make sure there are no lumps. Gradually add the egg yolks whilst whisking or stirring all the time. Mix in the candied peel if using. The mixture should turn very smooth and a warm yellow in colour.
In a separate bowl whisk the egg whites until they start to form soft peaks. Slowly add the remaining sugar whisking all the time, until the sugar has dissolved.
Start incorporating the whisked eggs into the cheese cream by adding first a third of the whisked egg whites and folding it gently using circular movements from the bottom to the top.
Fold the remaining egg whites into the cheese mixture the same way as above.
Pour everything into a spring form tin (25-26 cm in diameter) laid with baking parchment.
Bake in a preheated oven to 180 C (static oven) for about 35-40 minutes.
If during baking the top of the cake turns brown very fast, loosely cover it with some aluminium foil.
The cheesecake should look light and plump and have some wobble to it when moving the tin.
Take your cheesecake from the oven and allow it to cool down and set for a minimum of 2 hours.
Decorate with icing sugar and grated lemon zest.