In a heavy based sauce pan, sweat onion, garlic and mushrooms in a little olive oil. Add rice and sweat till almost transparent.
Add white wine and reduce till liquid is almost gone, before gradually adding more stock, small amounts at a time, stirring constantly between each addition.
When rice is cooked and al dente, has a slight crunch to it, remove from heat, add lemon juice, add cold diced butter, parmesan, thyme and season to taste. Add a splash of white truffle oil if desired.
Set in roasting tray and cool.
Once cooled, roll into bite sized balls and coat with fine polenta, deep fry or brown in fry pan with little olive oil.