Lightly grease a large baking tray with olive oil.
Place the wine and saffron in a cup. Stir briefly then let it sit.
Melt the butter in a large frypan over medium heat. Add the onion and stir for 3 minutes or until transparent. Mix in the rice and continue cooking and stirring until the rice has absorbed most of the butter.
Slowly stir the white wine and saffron into the rice. Stir continuously until the wine is absorbed and rice is creamy. Season with thyme. Pour in 1 cup of chicken stock at a time, cooking and stirring constantly until each cup of stock is absorbed before adding the next. Stop adding stock when the rice is tender. If you run out of stock you may use water. Remove from the heat, stir in the parmesan cheese and allow to cool until you can touch it without burning your hands.
Pour the rice mixture out onto the greased baking tray and spread evenly. Chill in refrigerator for about 1 hour.
When the rice is cool roll small portions into balls about the size of golf balls. Tuck a cube of fontina/gruyere cheese into the centre of each one. Roll each ball in breadcrumbs to coat.
Heat the olive oil in a heavy saucepan or deep fryer to 180 degrees C. The oil should be about 8cm deep. When the oil is hot fry the arancini until they reach a golden orange brown colour; about 3 minutes. Arancini literally means 'little oranges'. Cool and drain on paper towels for 5 minutes then serve with any marinara sauce.