Heat 1 tablespoon olive oil in a medium pot. Add mushrooms, season with a little salt and pepper, and cook over medium high heat until mushrooms just start to soften.

Add the chicken broth and thyme, bring to a gentle simmer.

As the broth is heating:

In a large pan, sweat onions in remaining olive oil until translucent. Add garlic and rice, stir well.

Add half of the wine, stirring until wine is almost completely absorbed by the rice. Repeat.

Add simmering stock, about ½ cup at a time, stirring constantly. As rice absorbs one ladle of stock, add another and continue stirring.

Once rice is almost cooked, season with salt and pepper to taste.

Stir in grated cheeses, just until well incorporated and smooth. Remove from heat, allow to cool to room temperature.

Whisk egg, add to the cooled risotto mixture along.

Cover with plastic wrap and chill for several hours - ideally overnight.

Line a work surface - and a baking sheet - with parchment paper.

Mix together the flour, salt, and thyme into one medium bowl. Crack the eggs into a separate bowl, whisking until lightly beaten and smooth. Measure the panko into a 3rd bowl.

Using 2 Tablespoons, scoop small portions of chilled risotto out onto your work surface. Aim to be scooping consistent amounts, so your risotto balls are the same size. I usually get 40-42 pieces.

Once all of the batter is scooped, use clean hands to roll each into a ball, then into the flour mixture.

Dip a flour coated rice ball into the beaten eggs, allow the excess egg mixture to drip off before rolling it in the panko, giving it a light squeeze to compact the coating a bit. Place on the lined baking sheet,

Repeat with remaining rice balls. I like to use my left hand to dip a risotto ball into the egg, then drop it into the panko. Then I use my right hand to coat the ball with panko - this prevents a buildup of coating from forming on my hands!

Once all the balls are coated, place the cookie sheet of coated balls in the fridge to chill, as you prepare the oil.

Heat oil 375 F (190 C). You can use a deep fryer, or a heavy pan. If not using a deep fryer, use a deep, heavy pot, filled to at least 3" deep.

Carefully transfer chilled arancini to the heated oil. Fry a few at a time - turning frequently for even cooking- until golden brown.

As the mini mushroom arancini are cooked, use a (metal!) slotted spoon to transfer them from the oil, to a pan lined with paper towels.

Serve hot, with marinara sauce for dipping.