Combine the milk, water, 30 g butter, and a pinch of salt in a 3-quart / 2.8L saucepan. Bring to a boil over medium heat.

Pour in the semolina in a steady stream, whisking constantly to avoid lumps. Cook for 3 to 4 minutes, stirring, until the mixture thickens and pulls from the sides of the pan.

Remove from heat and let the semolina porridge cool for 15 minutes, stirring occasionally so a skin doesn't form on top.

Heat the oven to 180C / 356F. Grease a 26 cm / 10-inch springform pan with butter and dust with a spoonful of semolina, tapping out the excess.

In a large mixing bowl, beat the ricotta and sugar together until smooth, with no lumps of ricotta left.

Add the eggs one at a time, beating well after each addition. Stir in the lemon zest, orange zest, vanilla extract, and cinnamon if using.

Fold the cooled semolina porridge into the ricotta mixture in two additions, mixing until the batter is smooth and pale yellow.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake for 50 to 60 minutes, until the top is golden and a toothpick inserted in the center comes out clean, with only a slight jiggle underneath.

Turn off the oven and let the cake sit inside with the door cracked for 10 minutes, then transfer the pan to a wire rack.

Cool completely at room temperature, at least 3 hours, before removing the springform ring. Chill further if you have time.

Dust with powdered sugar and slice into wedges to serve.