Mosterdsoep (Groningen Mustard Soup)

Name: Mosterdsoep (Groningen Mustard Soup)
Prep time: 15 min
Cook time: 30 min
Total time: 45 min
Yield: 4 servings
Cuisine: Dutch
Ingredients: 40 g butter; 40 g plain flour; 1 litre vegetable or chicken stock; 3 tbsp coarse mustard; 1 leek; 150 ml double cream; 150 g smoked bacon lardons; 1 bunch chives; to taste salt and pepper

IVSoups

Prep: 15 min
Cook: 30 min
Serves: 4
Level: Beginner

Groningen, the clay-rich province of the far north-east, gave the Netherlands two things the rest of the country happily borrowed: a tradition of mustard milling, and the pale, creamy soup that shows it off. Mosterdsoep is now on menus across the country, but its home is here, in a region that ground its own mustard seed and folded the result into nearly everything.

A soup with a mill behind it

The northern towns kept working mustard mills into the modern era, and the local coarse-ground mustard — sharp, seedy, unshy — is the soul of the dish. This is not a soup that hides its main flavour behind cream. The cream is there to round the edges, but the mustard is meant to be tasted, a clean bite that catches the back of the throat and is then soothed by the smoke of the bacon.

Cream to soften, smoke to deepen, mustard to bite — the whole soup is a balance of three notes.

Heat is the enemy

The one technical trap is temperature. Mustard's pungency lives in fragile compounds that turn flat and bitter when they are boiled, and cream will split if pushed too hard. So the roux and stock do their work first, over real heat, and the mustard and cream go in only at the end, warmed through and never boiled. Get that right and the soup stays smooth, bright, and unmistakably northern.

Finish generously — crisp bacon, a snowfall of chives — and serve with bread to catch what the spoon misses.

From the kitchen

“Never boil the soup after the mustard goes in — heat turns mustard bitter and can curdle the cream.”

Ingredients

Serves 4

The soup

40 gbutter
40 gplain flour
1 litrevegetable or chicken stock — hot
3 tbspcoarse mustard — Groningen or grainy
1leek — white part, finely sliced
150 mldouble cream

To finish

150 gsmoked bacon lardons — spekjes
1 bunchchives — snipped
to tastesalt and pepper

Method

1
Fry the bacon
Fry the bacon lardons in a dry pan until crisp and golden, then lift them onto paper. Leave a little of the rendered fat behind — it carries the smoke that mustard soup leans on, and a spoon of it can go into the roux.
2
Make a pale roux
Melt the butter in a heavy pan, stir in the flour, and cook gently for two minutes until it smells nutty but stays blond. This blond roux thickens the soup while keeping its colour light and its taste clean.
3
Whisk in the stock
Pour in the hot stock a ladle at a time, whisking hard between each addition so no lumps form. Add the sliced leek and simmer 10 minutes, until the leek is soft and the base has thickened to a light velvet.
4
Add mustard off the boil
Lower the heat and stir in the cream, then the mustard. Do not let it boil once the mustard is in — high heat turns mustard bitter and can split the cream. Warm it through only, and taste for salt and pepper.
5
Serve topped
Ladle into warm bowls and scatter each with crisp bacon and plenty of snipped chives. A little extra mustard swirled on top is welcome for those who like the heat sharper.

With the soup

A bowl of snert is a meal — but the trimmings make it Dutch.

Roggebrood met spek — rye bread with a slab of bacon
Katenspek — smoked cured bacon on the side
Mustard — a dab of coarse mustard on the rye

How a Dutch meal is built →

Questions from the kitchen

What mustard should I use?+

A coarse, grainy mustard is traditional; Groningen has its own famous mustard mills. Use a good wholegrain and adjust the amount to taste, stirring the last of it in off the heat.

Can I make it vegetarian?+

Yes. Use a good vegetable stock and swap the bacon for fried croutons or a handful of toasted seeds. The mustard and cream carry the soup on their own.

Why did my soup turn bitter?+

It boiled after the mustard went in. Mustard's pungency comes from volatile compounds that turn harsh and bitter with prolonged heat, so add it late and keep the pot below a simmer.