He has 16 sandwiches on his menu, but is happy to customise each one of them to his patrons' tastes. Sanjay Singh will put only beetroot and cheese in one; butter and powdered masala (salt, black salt, cardamom, cumin, and coriander seeds ground together) in another; tomatoes and garlic chutney for people who want that mix; and capsicum and butter for a few others. Like most sandwichwallahs in our city, he assembles exactly what the customer desires – easily a few hundred combinations drawn from the handful of ingredients he has bought and barely processed. No restaurant affords the level of customisation to a snack, or meal, as a Mumbai rasta sandwichwallah.

Kala Ghoda-based sandwich maker Singh started out working at his elder brother's sandwich stall 18 years ago, as soon as he arrived from Benares. He was 12 then and the menu listed two items: vegetable sandwich and vegetable toast. They served about 100 sandwiches a day. Today, the daily average is 350 sandwiches and toasties, almost each one minutely customised. The Kala Ghoda Arts Festival in February is boom time; they sell 700 items a day during the event. Singh, who has since taken over the running of the stall from his brother, works with three other people on any given day. He calls them "mere bhai", but that's an ambiguous description. In truth, they are cousins, nephews, or people from his gaon (village).

Singh wakes up every morning at 5am, makes the chutneys for his sandwiches and travels from his home in Bhayander to Kala Ghoda where he sets up his stall at 9am. Before he opens shop, he buys vegetables from the Bora Bazar market in Fort. The breadwallah (who also supplies the ketchup) and coalwallah visit his stall daily to provide the remaining supplies. Singh emphasised to us the importance of a good workstation. The cutting surface must be at the right height, and there should be enough storage room for veggies and bread as well as the leftover trimmings that will be given away to street kids at the end of the day. All the ingredients must always be at arm's length. A folding table hinged to the side of the stall is part of the assembly line. Singh slides the sandwiches to his co-worker Gopal Singh, who fans the coal burner, flips the chimta, and stacks the ready-to-eat toasts.

Like most sandwichwallahs in Mumbai, the Singhs are deeply loyal to their brand of bread. Only Wibs is good enough for them. Britannia bread tends to have holes in it and is too tangy, according to Sanjay Singh. However, his "bhais" and he don't eat their own sandwiches for lunch. Singh's nephew comes to the stall with their dabbas (lunch boxes) at around lunch time and works at the stall for the rest of the day. There is a small steel stool behind the work area, and the bhais take turns for their lunch breaks. When they need to use the loo, they go to Jehangir Art Gallery and buy a token. They leave for home at 9.30pm after Singh stores the stall near a friend's shop in a nearby lane; he gets to bed at midnight at the earliest.

The stall is open 364 days a year; its annual day off is Holi. Over the past 18 years, Singh has had his stall remade four or five times either because the old one got worn out, or because he needed a larger space for his growing business. Singh is keenly attentive to the demands of his customers. "Jab log demand karte hain, toh hum nayee cheez shuru karte hain," says Singh, who started making sandwiches with brown bread three years ago when regulars started demanding it. When passers-by started asking "Grill hai kya?", Singh – who still makes most of the toasts in a "chimta" press over coals – saved money to buy a grill and started serving Right Place-style veg cheese sandwiches two years ago. Singh's observations of market trends also led to the addition of the two most fancy (and strange) items on the menu – the Chinese toast with chopped veggies and Szechuan sauce, and the Russian toast, which is the Chinese one plus beetroot and potatoes.

Sandwich making by numbers (consumed per day)

Green chutney: 7 kilos

Garlic chutney: 4 kilos

Butter: 3 kilos

Loaves: 35

Potatoes: 20 kilos

Tomatoes: 17 kilos

Cucumbers: 15 kilos

Onions: 15 kilos

Garlic: 4 kilos

Capsicum: 2.5 kilos

Beetroot: 4 kilos

Cheese: 4 kilos

Coal: 7 kilos

Raddi paper for serving and wrapping: 2 kilos

Cheapest sandwich: Aloo slice for 13 rupees (14p)

Most expensive sandwich: Samosa cheese grill for Rs60

Best-selling item: Vegetable toast without cheese, about 200 a day

Number of veg toasts ready-to-eat at all times: 10-12

Size of the tarpaulin put up on rainy days: 15ft by 15ft

Amount of salt to make masala: 4 kilos a month

Hours spent working every day: 16.5