Chill the Risotto: Make sure your risotto is completely cold and firm, preferably chilled overnight in the fridge. Cold rice holds its shape much better when rolling. Stuff with Cheese: Scoop about 1.5 to 2 tablespoons of cold risotto into your hands. Flatten the rice in your palm, place a small amount of filling (mushrooms, garlic, onion cooked together) and cheese in the center, and wrap the rice around the cheese to form a tight golf-ball-sized sphere. Wet your hands with a little water if the rice sticks. Set Up a Breading Station: Line up three shallow bowls. Put the flour in the first bowl, the beaten egg in the second, and the panko breadcrumbs in the third. Coat the Balls: Roll each rice ball first in the flour, dip it into the beaten egg to coat completely, and then roll it in the panko breadcrumbs, pressing gently so the crumbs stick. Fry Until Golden: Heat about 2 inches of oil in a deep frying pan or pot to 350°F (175°C). Fry the arancini in small batches for 4 to 5 minutes until they turn deep golden brown and the cheese inside melts. Drain and Serve: Remove the balls with a slotted spoon and let them drain on a paper towel. Serve warm with marinara or aioli.

Combine ingredients: Add the beef, pork, bread, egg, cheese, garlic, parsley, salt, and pepper to a large bowl. Mix gently: Mix the ingredients just until combined using your hands or forks to avoid a dense texture. Form balls: Use a cookie scoop for even portions and roll into golf-ball-sized balls with wet hands. Sear: Brown the meatballs in a hot skillet with olive oil for a crispy crust. Finish cooking: Simmer the seared meatballs in a rich marinara sauce until cooked through and tender.