Rinse the rice under running water, then put into a large saucepan along with the milk, over medium heat. Heat the milk gently, stirring occasionally for 5 minutes or so. Add the lemon zest, cinnamon stick and vanilla.
As soon as it begins to show signs of boiling, reduce the heat and very gently simmer the milk for 20 minutes. After the 20 minutes, remove and discard the lemon zest and cinnamon, then stir through the condensed milk and dulce de leche.
Stir continuously from this point until the rice is completely cooked through. This could be around 5 minutes.
Turn off the heat and allow the rice to cool to room temperature before decanting into individual ramekins, cups or one single dish.
Serve garnished with cinnamon and berries, if you like.