Pour rice into boiling water and cook according to producer’s instructions. Remove from heat, rinse with cold water, and let rice cool.
In a large bowl, mix the Ricottas with the beaten eggs and the sugar. Beat with a mixer until well combined and smooth. If using liqueur and zest, add now and continue mixing. Add cooled rice to the bowl and mix through with a wooden spoon.
Grease and line an oven dish or a round 23 centimetre springform tin with baking paper.
Pour ingredients in bowl into oven dish. Bake for one hour until golden.