A few years ago I went on a course entitled Green Onions. Run by an American called Booker, the course promised to get me slicing my onions at record speeds. There were two parts: the first, a four-day residential, focussed on spring onions in the Mediterranean style, whilst the second, a mere afternoon in a rustic kitchen, allowed us to move on to the trickier Vietnamese shallot. I, being a confident and somewhat cocksure young man, didn’t bother with the second: “I ain’t gonna be needing no shallots, Booker T”, I said. “You can take Donald and the Steves on your little merry-go-slice, but I’m off to make me a tabbouleh.”

So, armed with bulgur wheat, mint, parsley and coriander, a tabbouleh is what I magicked up, complete with a beautifully ornamented spring onion garnish. And it was popular – my friends, eager to taste the fruits of my new skills, stuffed themselves with my finely sliced tabbouleh: they were full as ticks. “Toby!”, they cried. “Where once you could not slice a bean, you now can slice for the Gods. We believe your slicing can be equated with the great Michelin chefs around the world. So forget your previous inabilities, for this tabbouleh is your own tabbouleh rasa.” And we laughed and laughed, for I understood there was a pun without having to quickly Google it.

After a month of sublime, eloquent slicing and hot, fresh tabbouleh one close friend of mine, recently back from Southeast Asia, asked me to make her a Bánh Mì sandwich. She’d eaten my tabbouleh with gusto almost every night, but was keen to relive the memories of Hanoi street food. “Not a problem!”, I cried. “I was going to consider moving on to a European cuisine, but Vietnamese has so much more to offer. Now, you go to Germany, you’ve got your Bratwurst, your Butterkuchen and your Braunschweiger. There, in Vietnam, you’ve got your Pho, your Tom Chien Xu and your Bun Cha Nem. And as you look around the world, you go to Russia, Great Britain, France – any country: everybody! Everybody is doing flips and twists just to tuck in to some genuine Vietnamese.”

So, loaded with pickled vegetables, many meats, lemongrass, a de-fluffed baguette and condiments I began my Bánh Mì preparation. The chicken, however, called for a marinade: nam pla, lime juice, soy sauce and – oh devil of devils – shallots.

How could I have been so dumb? How could I have been so naïve to assume that my one piece of expertly practised knife-work would get me through an evening of unfamiliar cuisine? And so, with my shallots firmly between my legs, I telephoned Booker T. “Booker”, I asked, “is it possible to tell me how to slice a shallot? I thought knowing how to slice a spring – sorry, green – onion would suffice, but I was wrong. So very wrong.”

“Young man”, he replied, “knowledge of how to slice only really begins to make sense when you have two things of which to link. Knowledge of how to slice a green onion is different to that of how to slice a shallot. The physical skills of both are similar, true, but you must know both first before you can practise, less you make mistakes.”

“I don’t mind making mistakes”, I said. “But Booker, I now realise that the more I know about slicing various onions the more well-equipped I will be when I face more obscure onions, like red onions, or the Cepa de Apa.”

“Fool!” shouted Booker. “You are not yet ready to slice the Cepa de Apa. It’s this kind of attitude towards knowledge that makes people think the Blues Brothers wrote the original. If you’d stayed in class you might have got all the references.”

And with that he put down his receiver. I had to learn the hard way, by YouTubing my way through hours of three-minute videos of poor advice.