Is it possible to use a Japanese rice cooker to cook the rice, milk and zest without any harm to the rice? Will it make the rice too tough?
Nigella's Rice Pudding Cake) (from COOK, EAT, REPEAT) is based on the Italian Torta di Riso. The arborio rice is cooked in a saucepan with milk and lemon zest, before being mixed with butter, sugar and eggs and baked.
It may be possible to cook the rice initially in a rice cooker, but it very much depends on the model. Some models of rice cooker suggest the rice should be cooked first with some water, which will not be suitable, whereas others have a "porridge" setting that can also be used to make rice pudding (usually you need to run this setting twice for rice pudding). Some models have "fuzzy logic", which can automatically adjust the cooking time and temperature for you. So we suggest that you consult the manufacturer's handbook to check if your model is suitable and which settings to use. Make sure that the rice has absorbed the milk and taste a couple of grains of rice to make sure that they are tender on the outside and with a slight firmness, but not chalky, on the inside.