Toast the rice in a dry pan over medium heat until slightly translucent. Deglaze with a splash of white wine. Season with salt and pepper, then gradually add hot vegetable broth, stirring often.
Halfway through cooking, stir in the tomato purée. Continue cooking until the rice is al dente and the liquid is absorbed.
Once cooked, stir in a knob of butter and the Parmesan cheese. Let the rice mixture cool completely until firm (you can refrigerate it for faster results).
Take a heaping tablespoon of rice in your hand, flatten it, and place a cube of mozzarella in the center. Shape the rice around the cheese to enclose it fully, forming a ball or oval shape.
Roll each ball in flour, then dip in beaten eggs, then coat with breadcrumbs. For extra crunch, repeat the egg and breadcrumb steps one more time.
Heat vegetable oil to 355°F (180°C). Fry the supplì in batches until golden brown and crispy, about 3–4 minutes. Drain on paper towels.
Serve hot, while the mozzarella inside is still melty.
