In a cool, marble-floored convent in Ronda, Andalusia, a cluster of nuns in floury habits are rolling sugary almond dough into cocktail-sausage-sized sweets. They’ve made 20 trays of 35 today, but 700 represents only a fraction of the 1,000kg they need to make by Christmas, when people will come from all over Spain to buy bags of them.

The nuns bake several tons of sweet biscuits a year / Images: Jospeh Fox

The uncannily holy-looking light shining through a high window onto the rolling table in front of them suggests they might be getting some divine help. There’s no rest for the wicked, but there’s no rest for the pure either. This convent of Franciscan nuns – also known as the Order of the Barefoot Franciscans – has been making “sweeties”, as they cutely call them, for centuries in this small, cobbled Spanish town, which is also famous for its majestic views down the hillside.

Until very recently, they did so behind closed doors. The sweet-toothed might have travelled miles to buy them, but they had to wait outside when they arrived. At the door, visitors are met by a menu of artisan sweets and a wooden-shuttered hatch that swings open to reveal something like a confessional lazy susan, with the sweets and payment swinging round one after the other.

An oven of shortbread-based mantecaos / Images: Jospeh Fox

Next to the menu is a blessing: Concede a quien llega tu alegria, a quien mora tu Paz, a quien sale tu Bendicion (‘Grant to those coming through this door your joy, those dwelling your peace, and those departing your blessing’). Yet while the nuns wish for your joy and peace, they haven’t wished to share the secrets of their sweet-making until now, when this particular convent has finally opened its doors, a bit like Willy Wonka’s chocolate factory to those with a golden ticket. But so far only one man has been inside and he isn’t Charlie Bucket.

José Pizarro, London’s most popular Spanish chef, found the convent last year and wrote asking for special permission to visit. “I knew that nuns made the best sweets in Spain, because they have been refining the recipes for centuries,” he says. “But I didn’t realise, at first, how secret the whole process is – I was rejected by seven other convents before I found this order. I have huge respect for them because, with fewer nuns in Spain, authentic sweet-making is a dying art and they want to keep the recipes alive. You can’t get anything that’s even close to the traditional best in the UK and the Spanish factory versions aren’t good, either.”