Historians in Prato have searched high and low for the true history of this local dish. We have one possible explanation (although this dish is delicious enough to not really need explaining), here it is:
Celery need a lot of care and attention to grow well. The cultivation process is quite complicated. The plants need constant watering and in fact they have grown well in the Prato area mainly thanks also to the abundant supply of water that came from the river Bisenzio. Consequently, this humble yet precious vegetable was treated well by Prato’s chefs who of course tried to find the most interesting ways to serve it, like stuffing it with delicate fillings.
Quickly boil 4 celery stalks and set aside to dry. Mix 300g minced veal, 150g minced mortadella, 1 tablespoon of chopped parsley, 1 small clove of garlic finely chopped, 2 eggs, grated parmigiano cheese, spices and salt and pepper. Fill each celery stalk with the mixture, tie the stalks together, dip them in flour and deep fry them. Once they are fried, place on kitchen roll to absorb the excess oil and place on a baking tray and pour either meat sauce or a simple tomato sauce over them. Cook in the oven. Once they are ready, sprinkle with grated parmigiano.
Source: APT di Prato