Although onion soups date back to Roman times, this particular soup began life in eighteenth-century Paris as a beef broth with caramelised onions on top. Now served without the beef, the quality of the onions is crucial. You want both high acidity and high sugar levels to create a fully-flavoured soup. The best onions are Rose de Roscoff. Spanish onions, although lacking in acidity, will also work. I like to float croutons on mine, and I grate some two-year-old Comté cheese on the top. And make sure you caramelise your onions to achieve a rich, brown colour. A Frenchman's heaven!
For the soup
Rose de Roscoff onions, or white onions, cut into 3mm slices
freshly ground black pepper
dry white wine, boiled for 30 seconds
caster sugar (optional)
For the croutons
12 x 1cm
Comté cheese (ideally two-year-old), grated
Preheat the oven to 170°C/Gas Mark 3½.
For the soup, put the flour into a small baking tin and toast in the oven for 30 minutes. Toasting the flour cooks the starch and develops a nutty flavour, which will add another layer of flavour to your soup.
On a high heat, in a large, non-stick saucepan, melt the butter without letting it brown.
Add the onions and soften for 5 minutes, stirring frequently.
Season with the salt and pepper.
Continue cooking the onions for 20–30 minutes to achieve an even, rich brown colour.
Stir every 2–3 minutes, and make sure you scrape any caramelised bits of onion from the base of the pan to prevent burning and achieve an even colour.
Once the onions are the desired colour, stir in the toasted flour and mix thoroughly to absorb all the juices.
Gradually stir in the white wine and one-third of the cold water and whisk to prevent lumps from forming.
Bring to the boil, add the remaining water and simmer for 5 minutes.
Taste and correct the seasoning, adding the sugar if required.
To make the croutons, heat your grill on a high setting.
Arrange the baguette slices on a baking tray and toast on one side for 3–4 minutes, until lightly golden.
To serve, divide the soup between serving bowls, top with croutons, toasted side up, and sprinkle over the grated Comté.
This recipe is adapted from the book Kew on a Plate
Accompanying a very special BBC TV series, Raymond filmed with the Royal Botanic Gardens, Kew, this is the story of the nation's favourite fruit and veg. You’ll find an array of mouth-watering seasonal recipes, detailed tasting notes, and valuable tips for growing your own produce from the talented gardeners of Kew. A perfect read for the green-fingered gastronome.