Bologna has a nickname, la Grassa, the fat one, and it has earned it. But this is also a city that takes its food seriously enough to write its recipes down and deposit them officially, like documents in a vault. The tortellini filling was deposited with a notary in 1974. The official width of a tagliatella was deposited in 1972, and the ragù recipe in 1982. Today you eat your way through all three. You start at the Mercato delle Erbe on Via Ugo Bassi, buy mortadella in the old market lanes and eat it with a glass of wine in an osteria that serves no food at all. Then you have tagliatelle al ragù facing the building that keeps the recipe, a glass of Sangiovese in a family-run grocer's shop and tortellini in brodo under the porticoes, and you finish with gelato on Via Castiglione. It is one of our self-guided walking tours, about 2.6 kilometers from start to finish, with about 35 minutes of actual walking and a great deal of eating in between.

Before you set off

Go Tuesday to Saturday, and start around 10:30 in the morning. The timing matters here. The wine shop at stop five, Antica Drogheria Calzolari, closes at 1:30 in the afternoon (it reopens at 4) and shuts completely from late July to the end of August. Drogheria della Rosa, the trattoria at stop six, is closed on Mondays and starts serving lunch at 1 o'clock, so book a table ahead. The pasta makers round the corner from the first stop are closed on Sundays. Many places in Bologna close for part of August, so a summer visit needs extra checking.

You pay for your own food as you go. There are seven stops and six of them involve something to eat or drink, including two sit-down pasta plates. That is a lot, so share plates and take small portions wherever you can. Pork, dairy, egg, gluten and nuts turn up in almost everything in this city, so if you have an allergy, ask at every counter. Hours change, so check before you go. The longest walk between stops is about 650 meters, so there is always a short rest coming.

Mercato delle Erbe

You're standing at the Mercato delle Erbe, the covered market on Via Ugo Bassi. Look inside at the stalls of fruit and vegetables, the meat and cheese counters, the fish, and the restaurants and wine bars that now share the hall with them.

This building is where Bologna's market came indoors. It was designed in 1910 by Arturo Carpi and the engineer Luigi Mellucci, and when it opened, the market stalls moved here for good from Piazza Maggiore, the city's main square, which is your next stop. The Second World War hit it hard. The market was heavily bombed and reopened in 1949. Then in 2014 it was restructured to add the restaurants, so today you can shop and eat under the same roof.

Now walk about 80 meters round the corner to Via Belvedere 7/b, and look through the window of Le Sfogline. A sfoglina is a woman who rolls fresh pasta by hand, and the shop was opened in 1996 by Renata Zappoli and her daughters Daniela and Monica. Watch them roll the dough thin and fold tortellini one at a time.

Remember those little rings, because they are the first recipe in the vault. On 7 December 1974, the Dotta Confraternita del Tortellino, a brotherhood founded in 1965, and the Accademia Italiana della Cucina deposited the tortellini recipe with a notary. The filling is fixed: pork loin, prosciutto crudo, mortadella, Parmigiano Reggiano, egg and nutmeg.

There is also a legend, and it is only a legend. An innkeeper in Castelfranco Emilia is said to have glimpsed the goddess Venus through a keyhole and copied her navel in pasta. Bologna and Modena both claim the dish.

What to order here: a coffee or a snack from one of the market counters. At Le Sfogline, just watch, and buy tortellini to take home if you're staying nearby.

From the market, walk east along Via Ugo Bassi, then turn right into the great square. It takes about seven minutes.

Piazza Maggiore

San Petronio basilica on Piazza Maggiore, Bologna

You're in Piazza Maggiore, the main square of Bologna. On one side stands Palazzo d'Accursio, the city hall. On another rises the huge front of San Petronio. There's nothing to eat at this stop, and that's the point.

Picture this square full of market stalls. Until the Mercato delle Erbe opened, this is where they stood: the city's food was bought and sold right here, in front of the city hall and the church. The move to the covered hall you just left cleared the square for good. So when you walk on from here into the narrow lanes to the east, you're following the market's old neighbors. Those lanes are the Quadrilatero, the medieval market district, and they still sell food today.

Take a moment to rest your appetite, too. You've had a coffee, and ahead of you are mortadella, wine, a plate of pasta, another glass, a bowl of tortellini and gelato. This square is the last place on the walk where nobody will try to feed you.

Here is the plan for the next stop, because it works in a way you won't find in many places. The osteria you're heading to sells only wine and beer. No food, and not even soft drinks. If you want to eat, you bring your own. So before you go in, you'll shop for your picnic in the lanes around it.

Head east off the square into the market lanes. Within about three minutes you reach a tiny alley, Vicolo dei Ranocchi, and the Osteria del Sole.

Osteria del Sole

You're in Vicolo dei Ranocchi, deep in the Quadrilatero. Around you is a grid of old market lanes: Via Pescherie Vecchie, Via Drapperie and Via Caprarie. In front of you is a plain old wine bar with no menu, the Osteria del Sole.

The osteria dates itself to 1465. That is its own claim: it says the first documents about it come from that year. What you can see for yourself is how it works. It pours wine and beer, and nothing else. Guests carry in their own food and eat it with a glass in hand.

So shop first, all within about 100 meters. Tamburini, at Via Caprarie 1, has been selling here since 1932, by its own account, with IGP mortadella, tortellini and Parmigiano on the counter. Salumeria Simoni is known for its mortadella called La Regina di Bologna, the queen of Bologna. Paolo Atti and Sons, at Via Caprarie 7 and Via Drapperie 6, sells tortellini, fresh pasta and bread.

Mortadella is the city's own sausage. Mortadella Bologna is protected across the European Union, with IGP status, and the rules say it must contain at least 15 percent cubes of pork fat. Those are the pale cubes you'll see in a slice. Pistachios are a modern option, so you'll find it both with and without them.

What to order here: ask the shop for a few slices of mortadella, carry them in, and order a glass of house wine at the bar.

When you're done, walk east out of the lanes and turn right down Via Castiglione. Sfoglia Rina is about three minutes away, near the top of the street.