There are many contenders for the most delicious sandwich in London, from the pork katsu sando at TaTa Eatery that cluttered your Instagram feed last year, to the salt beef Reuben at Monty’s Deli. But the carb crown surely belongs to the smoked eel sandwich at Quo Vadis. The legendary Soho eatery opened in 1926, but its star has shone brightest since 2012, when new owners, restaurateurs Messrs Sam, James and Eddie Hart, brought Mr Jeremy Lee on board as a partner. Since then, the flamboyant Scottish chef has cemented the restaurant’s reputation as one of the finest places to eat produce-led, classic British food in the UK. Mr Lee’s smoked eel sourdough sandwich, laced with horseradish and mustard, is a permanent fixture on the regularly changing, illustrated menu, and a Quo Vadis signature. It was an obvious choice, then, as the first instalment of our series in which acclaimed London chefs share the recipes for – and the stories behind – their most iconic dishes.

“My love affair with smoked eel began at Alastair Little,” says Mr Lee, who cooked at the trailblazing Soho restaurant before taking a job at the Blueprint Café, where he stayed for 18 years. “Over the years, I started making dishes with smoked eel. The smoked eel sandwich made a rare appearance at the Blueprint Café, although in a very different guise to the little darling that we put on the menu at Quo Vadis.”

Mr Lee’s sandwich is made with just five ingredients: sourdough, butter, smoked eel, Dijon mustard and fiery horseradish cream. It’s served with pickled red onions, which help cut through the smoky fish. Sourcing the correct ingredients is imperative, says Mr Lee. “This is so curious a recipe, for it is the very essence of simplicity. But it must have bread from Poilâne [a French bakery]. We’ve always bought the smoked eels from the Devon Eel Company – it’s a very lovely enterprise, devoted almost exclusively to the skilled craft of smoking an eel. The horseradish is grated fresh, as its potent heat diminishes swiftly. And I use the best butter available.”

When it comes to constructing your sandwich, Mr Lee advises being bold with the ingredients. “Every cook who is groomed to make this sandwich always hesitates when he sees the quantities of horseradish, mustard and pickles. The ingredients and quantities used only make sense when brought together in the sandwich, just so.”

The smoked eel sandwich speaks of Mr Lee’s ability to create dishes that taste of so much more than the sum of their parts. “At Quo Vadis, we are devoted to produce and ingredients,” he says, “and talking constantly to producers, growers and makers of delicious things. These ingredients delight when they arrive in the kitchen, and inspire recipes that seem simple, but in fact have enormous thought and effort behind them.” The dish, says Mr Lee, “is prepared so simply, it allows all the ingredients to taste of themselves,” meaning, “it is a very joyful business.”

And to drink? “If you’re being very indulgent and having a smoked eel sandwich while perusing the menu, a Quo Vadis martini is vital,” says Mr Lee. “At the beginning of lunch and dinner, a splendid muscadet is a good choice.” Try London’s most celebrated sandwich yourself with Mr Lee’s recipe, below.

• 1 pinch of sugar
• 2 tablespoons of good white wine vinegar
• 1/4 small red onion, peeled and thinly sliced
• 1 slice of sourdough bread (ideally from Poilâne bakery)
• Butter
• 1 heaped teaspoon of Dijon mustard
• 30-40g fillet of smoked eel (ideally taken from an intact fish)
• 1 heaped teaspoon of horseradish cream, of a fiery temperament

Combine the sugar and vinegar together in a pan and gently heat until the sugar dissolves. Remove from heat and steep the sliced onion in the pickle and let stand for an hour or so.

Warm a griddle pan over gentle heat. Once hot, lay the slice of sourdough bread on the pan and brown nicely.

Generously spread butter on the toasted side of the bread, followed by Dijon mustard, then cut the piece of toast in half.

Cut the eel into three even pieces and place on top of one of the toasted sides of the bread. Add horseradish cream on top and place the second half of bread, with the toasted side down.

Return the sandwich to the griddle pan and grill on one side until brown. Carefully flip the sandwich and grill for a further few minutes.

Drain the pickled red onions and serve alongside the sandwich.