Step 1: Heat olive oil in a large saucepan or Dutch oven over medium heat. Add the chopped onion and sauté until softened, about 5 minutes. Add minced garlic and cook for another minute until fragrant.
Step 2: Stir in the Arborio rice and cook for 2 minutes, ensuring all grains are coated. If using, pour in the white wine and stir until completely absorbed.
Step 3: Begin adding the hot vegetable broth, one ladleful at a time, stirring constantly and allowing each addition to be fully absorbed before adding the next. Continue until the rice is creamy and al dente, about 20-25 minutes.
Step 4: Remove the risotto from heat and stir in the Parmesan cheese and butter. Season with salt and pepper. Spread the risotto onto a baking sheet in a thin layer and cool completely in the refrigerator (at least 2 hours, or overnight).
Step 5: Set up your breading station: Place flour in one shallow dish, beaten eggs in another, and Panko breadcrumbs in a third.
Step 6: Take about 2-3 tablespoons of cold risotto and flatten it into a disc in your palm. Place a mozzarella cube in the center. Carefully mold the rice around the cheese to form a tight ball, ensuring no cheese is exposed.
Step 7: Roll each rice ball first in the flour, then dip in the beaten egg (allowing excess to drip off), and finally roll in the Panko breadcrumbs, pressing gently to ensure an even coating. Repeat for all arancini.
Step 8: Heat vegetable oil in a deep pot or Dutch oven to 350-375°F (175-190°C). Fry the arancini in batches, being careful not to overcrowd the pot, until golden brown and crispy, about 4-6 minutes per batch.
Step 9: Remove the fried arancini with a slotted spoon and place them on a wire rack set over paper towels to drain excess oil. Serve immediately with your favorite marinara sauce.