Bring water to the boil with stock cubes and saffron. Add the rice and cook for about 10 minutes, stirring from time to time. At the end, there should be almost no water left. Add the butter, Parmesan, and stir.
Transfer the rice into a large plate, cover with a clean tea towel and let sit overnight.
Bolognese sauce (the day before):
Heat a little oil and butter in a large frying pan and pot and cook the mince till evenly browned. Add onion and fry till translucent.
Add the tomato puree, passata, a little water, salt and pepper. Stir and add the peas, carrot and celery.
Cook till the water has almost completely evaporated. Place in the refrigerator overnight.
Arancini (the same day):
Dice the hard-boiled eggs and ham into 5mm pieces. Dice the mozzarella balls into 1cm pieces.
Take a about half golfball size amount of rice in the palm of the hand and make a little hollow.
Add some ham.
Add some mozzarella.
Add 1 teaspoon bolognese sauce.
And some egg.
Enclose the filling with the same amount of rice and shape into a tightly packed ball by rolling it with your hands. Repeat till all the ingredients are used up.
Mix the flour with some water till the mixture has the consistency of crepe batter. Coat each rice ball with this mixture.
Spread the breadcrumbs on a large tray and roll the rice balls, 4 to 6 at a time, till well coated.
Heat oil to 180 C and fry the rice balls till golden brown, 4 to 5 at a time.
Remove from the oil and degrease on kitchen paper.
If served as starters, make the rice balls a little smaller.