People who love red-bean cakes often say Japanese sweets are healthy, but the truth of course is, they’re loaded with sugar. That’s what helps preserve them, says Mari Masuda, the madame of Tokutarou sweets bakery. She also lets you know, without a hint of reserve, that she is aged 74. You can’t help thinking … she must be both very sweet and healthy! And why wouldn’t you be proud?

She apologises for her English, although of course there is no need to, since you are in her world. When you ask what’s special about the enigmatic cube-shaped sweet with the white crust, she gives a quick lesson in how they are made: shaped from beans that are sugar-simmered in their skins, unlike most of the other fillings for which the beans are peeled. Then coated with an envelope of flour, water and salt, and baked on a tray of copper, not iron, as iron heats unevenly.

They are called kintsuba. Tokutarou’s kintsuba are famous for not being too sweet. That’s why Madame Masuda suggests you eat them promptly. The sweet itself is like a primitive, modernistic, asymmetrical, dumpling-size block. It seems to hover in outer space, its wonky edges and airy grey-white skin stretched tight and bubbly over its unctuous purple insides. Bite through the slight resistance of the covering, and the texture is warm, smooth, grainy and wholesome. They cost mere pennies, less than 150-yen for one. You can buy some for friends and eat one in the corner by the window, where there is a bench and a water cooler.

The shop in Asakusa 3-chome has been running for a century and a half, and Madame’s grandson, aged 9, is on track to be the fifth generation. It is also their home, recently rebuilt in a contemporary-traditional style. You would have walked straight past if you hadn’t got talking to the master, having a smoke break outside his kitchen.

Customers come in and chat loudly. The wooden seat and water are welcoming, and Madame offers you some alcohol hand wipes when you ask if you can eat a sweet at the counter. The atmosphere is old-world, reminiscent of Kyoto in its elegance but there is a sense of something spontaneous, something more fun. Somehow it feels a lot like Edo.