Rome — supplì are documented in Roman sources from the 19th century. They are the definitive Roman fried snack, sold at frittorie and pizzerie throughout the city. The name 'supplì al telefono' for the cheese-string version is a modern addition; historically they were simply supplì.
Supplì (from the French 'surprise') are the Roman street-food croquettes — oval portions of rice cooked in tomato-based ragù (or leftover risotto), stuffed with a cube of mozzarella, breaded, and deep-fried until the exterior is golden and crispy and the mozzarella inside has melted to a molten pool. When the supplì is pulled apart, the melted mozzarella stretches in strings between the two halves — the 'telephone wires' that give the preparation its full name, supplì al telefono. The preparation belongs to the friggitoria tradition of Rome — the fried food shops that supply the Roman street food.
A supplì pulled apart at peak heat reveals the cheese-string — the melted mozzarella stretching between the two halves in white, silky threads. The exterior crackles; the rice interior is tomato-fragrant and slightly sticky; the mozzarella at the centre is completely molten. Eaten standing on a Roman street, it is the most satisfying Roman fast food.
Make a rice base: fry rice in a soffritto of onion; add crushed tomatoes and beef broth; cook risotto-style until al dente; stir in Parmigiano and allow to cool completely. The rice must be cold for shaping — warm rice is too sticky. Divide into portions of 80-100g; flatten; place a cube of fresh mozzarella (or fior di latte) in the centre; form into an oval shape, encasing the mozzarella completely. Flour lightly; dip in beaten egg; coat in fine breadcrumbs; press firmly. Fry in neutral oil at 175°C for 4-5 minutes until deep golden. Rest 1 minute. Pull apart at table to reveal the cheese string.
The rice should be flavourful on its own — it is not merely a vehicle for the mozzarella; a well-made tomato-ragù rice is the base. Some Roman frittorie add a slice of prosciutto or salame inside with the mozzarella. Supplì are best eaten within 2 minutes of frying — the mozzarella re-solidifies quickly. The classic accompanying drink in Rome is a cold beer.
Rice not cold — warm rice won't hold its shape when formed and the shaping is impossible. Mozzarella too wet — fresh mozzarella must be sliced and drained on kitchen paper for at least 30 minutes before use; wet mozzarella produces a watery centre and can prevent the exterior from crisping. Frying at wrong temperature — too cool and the breading absorbs oil; too hot and the outside burns before the interior is hot.
Anna Gosetti della Salda, Le Ricette Regionali Italiane; Giorgio Locatelli, Made in Italy