The Prince of Wales and Duchess of Cornwall read a copy of a British newspaper when they arrived in Austria - through a gossamer thin sheet of pastry.
Charles and Camilla were shown the test used by pastry chefs making the perfect apple strudel during a behind-the scenes tour of Cafe Demel, one of Vienna's treasured coffee houses.
The royal couple are coming to the end of a nine-day tour of Europe and arrived in the Austrian capital from Rome.
The trip has been widely viewed as a Brexit diplomacy tour with Charles and Camilla's presence reassuring the continent that the UK is still committed to its European neighbours as Britain leaves the EU.
The royal couple watched fascinated as head chef Oliver Csapo and his team made the cafe's signature apple strudel, Sacher Torte and hand-made tea and cheese biscuits.
Mr Csapo slipped a copy of The Times newspaper under the pastry to check its thickness, and with the words clearly visibly, it passed the test, he told the royal visitors: "I always have a paper handy."
As the chefs rolled out the mixture and made up the strudel before baking it in the oven for 25 minutes, Camilla, in a navy Fiona Clare coat dress, watched intently.
"It looks quite simple but I bet it's very difficult," she said.
Mr Csapo asked her if she liked baking and eating pastries and she mentioned her son Tom Parker Bowles, a successful chef. "I like it. I have a son who does the baking."
The royal couple did not try the strudel or have a go at making any of the products themselves but the prince had a small pastry upstairs when they sat down to a cup of tea and a chat with some apprentices.
Founded in 1786, the cafe carries the title K&K Hofzuckerbackerei, a royal warrant dating to the time of the Habsburg Monarchy, which fell at the end of the First World War after ruling Central Europe for 600 years.
In the evening Charles and Camilla were guests of honour at a state banquet staged at Vienna's Hofburg Palace with a range of guests from the environmental activists and fashion designer Dame Vivienne Westwood to sustainability campaigners.
Dame Vivienne, who attended the event with her partner Andreas Kronthaler, said: "I've met Prince Charles several times because I'm an activist for the environment and he's a big worker for the good of the environment, and we've been trying to save the rainforest and we will do.
"I've come especially because I'm a friend of Prince Charles and especially it's wonderful we've got this green (Austrian) president it will make a difference - it might save the world."
Camilla wore a chic Anna Valentine cream and gold chiffon dress while the Prince wore a dinner jacket and black tie.
There were around 100 guests at the event hosted by Austria's President Alexander Van der Bellen and diners enjoyed the boiled beef dish tafelspitz, a classic Austrian meal, a fish course and for dessert was apricot strudel.