In a large saucepan melt the butter and olive oil, then sweat the onions; add the rice and stir to coat well and lightly toast. Deglaze the pan with the white wine. Add the vegetable stock one ladle at a time, stirring constantly and waiting for the liquid to absorb before adding more. When the rice is finished, pull off of the heat and stir in the parmesan and season with salt. Pour onto a sheet pan and cool to room temperature or chill in a walk-in for at least two hours.
Mix together the herbs, nutmeg, cloves, 4 tablespoons of salt, and pepper to create a spice mix. To form the arancini, use a 1-ounce ice cream scooper to portion the rice, then place one piece of cheese in each and season with the spice mix. Roll into a tight ball, making sure to encapsulate the cheese; dredge the ball in the flour and polenta. Fry until crispy, making sure to fully melt the cheese; drain on paper towels. Sprinkle with salt and serve immediately.