Roasted onion, leek, garlic and potato soup

French onion soup is best made from onions that have been well roasted to intensify their sweetness while the ensuing caramelisation adds nuttiness and that umami that roasting brings. But that’s only the start.

The onions are chopped and go into a strong beef broth to simmer until their flavours are dreamily enticing. Then it’s finished with plenty of grated parmesan and browned.

There’s a garlic version of this too, quite similar but of course all about garlic, not onions.

Leek and potato soup is simpler but madly moreish in its own way. I’m talking about the hot version here, though vichyssoise, the cold alternative, has its own charms.

I had onions, and whole garlic heads, but I also had plenty of leeks. What to do? On Sunday I woke up with a brainwave, or what passes for a wave in my brain. Instead of either roasted onion or roasted garlic soup, I would make roasted allium soup, roasting all three – onions, leeks and garlic – and then turn them into a soup.

But... out of the blue came a curveball. The Foodie’s Wife was a tad crestfallen. What was wrong? “No, it’s okay,” she said, “I just fancied leek and potato soup...”

Ah. Then the recipe would be adapted. And that is how this ended up as a hybrid between roasted allium soup and leek and potato soup. And it was souper delicious.

This is how recipes are made! For some of us, this is exciting stuff. And here is the ensuing soup...

Tony’s roasted onion, leek, garlic and potato soup

(Serves 4 to 6)

Ingredients

2 large onions, peeled and halved

8 leeks trimmed, trimmed, rinsed and sliced

1 head of garlic sliced in half through the middle

4 medium potatoes, peeled and quartered

6 sprigs thyme, and more for garnish

2 litres beef stock

Salt to taste

Black pepper to taste

2 heaped tsp cornflour dissolved in water

Method

The onions in this soup have to be roasted before going into the pot. So have the leeks, and the garlic, but not the potatoes. But the three alliums are roasted for differing times, and sometimes at different temperatures.

And that part of it happens in an air fryer.

The onions are sliced in half through the middle, oiled and roasted until fairly tender. Then they have to be cooled so that you can handle them, and then you chop them up.

Leeks are a different kettle of allium. Notoriously, they will almost inevitably have a bit of soil under their top ends, in other words, the opposite of their root ends. The usual way of doing this is to make a deep cross in that end and run it under cold water while rubbing them to dislodge any soil.

Instead, I trimmed both ends, cut away the harder, greener parts of the leeks, and sliced them into slim rounds. I put them all in a colander and ran lots of cold water through, tossing them around with my hands in the running water. Then I left them to drain.

The whole head of garlic needs to be sliced in half right through the middle so that you have two rounds. Don’t peel it first; the husks protect the flesh, and you’re looking for that to be soft and oozy, not dry.

Everything has to be oiled, but not heavily, as they will be roasted in an air fryer:

• Add about 3 Tbsp olive oil to an air fryer basket (without the rack inside it), add the sliced leeks and toss.
• Place the halved onions on top of the leeks, cut side up, and oil the cut side lightly.
• Place the garlic rounds between them, also cut side up, and oil the cut side lightly.

Roast at 200°C for 10 to 15 minutes, then open the drawer and stir the leeks with a wooden spoon, placing the onion and garlic upright again once you’ve done so.

Cook for another 5 minutes, then remove the onions and garlic using tongs. Remove the leeks to a side dish.

Place the onion and garlic halves back in the basket and cook at 180°C (yes, lower the temperature) for another 5 minutes.

Remove the garlic to a cutting board. Return the onions to the machine for another 5 minutes at 180°C.

Meanwhile, peel the potatoes, put them in a deep pot of lots of cold water, salt moderately well, and bring to a boil. Boil until the potatoes are soft, then tip into a colander. Tip them straight back into the empty pot, and mash them. (No need to stir in butter or milk.)

Presuming that all of the alliums are now roasted, chop the onions and add them to a deep, heavy soup pot.

Add the 2 litres of stock, and stir.

Chop the roasted onions and add them.

Squeeze out each little bit of garlic from their half-husks, directly into the pot. Stir immediately.

Add thyme sprigs, reserving a couple for garnishing the soup.

Season with salt and black pepper, and stir.

Bring to a boil and reduce to a simmer. Cook for about 20 minutes.

Dissolve the cornflour in water, just to cover, in a ramekin, stirring vigorously with a teaspoon until it is fully dissolved.

Pour this into the soup while stirring with a wooden spoon.

Serve with thyme leaves scattered on top. DM

Tony Jackman is twice winner of the Galliova Food Writer of the Year award.

Follow Tony Jackman on Instagram @tony_jackman_cooks.