Put the milk, water, butter, salt, and lemon peel in a pot and bring to a boil.
Remove the lemon peel and add the semolina while stirring continuously.
Cook the semolina for 10 minutes, stirring constantly. If lumps form, use a stick mixer to remove them. Let the mixture cool slightly.
In the meantime, whisk the eggs with the sugar until pale. Whisk in the ricotta and vanilla extract. Stir in the limoncello if you’d like a hint of citrus, then mix until smooth.
Add the lukewarm semolina to the ricotta mixture and whisk until smooth and well combined.
Pour the batter into a greased 22 or 23 cm – 9 inch round springform pan.
Bake in a preheated oven at 180°C – 355°F for 60 minutes. It will be slightly wobbly, like a cheesecake.
Let it cool completely, then unmould, dust with icing sugar, and serve.
