Prepare the pasta matta dough first. Put the flour, water and olive oil in a blender and blend until combined, then wrap in cling film and let it rest in the fridge for at least 30 minutes.
Bring the milk to the boil, add a little salt, then add the rice. Cook gently until the rice is almost done — it should be very al dente. Take it off the heat and let it rest for about 15 minutes; the rice will finish cooking and absorb most of the milk. The mixture will still be very liquid at this point — that's fine, don't worry about it.
Preheat the oven to 180°C. Add all the remaining filling ingredients (ricotta, Greek yogurt, eggs, grated Parmesan, margarine, nutmeg and salt) to the rice and combine well.
Take the dough out of the fridge and roll it out into a thin sheet larger than the baking tin. Lay it into the lightly greased tin, letting the edges overhang. Pour in the mixture, which will still feel rather soft, then fold the excess pastry edges inward — they will cover most of the cake, but not all of it.
If you like, brush a little egg wash over the top. Bake in the preheated oven for about 30 minutes, or until the surface is golden.