Grüne Soße (literally: green sauce) is a fresh herb sauce made with some or all of seven specific herbs – sorrel, chervil, chives, parsley, burnet, cress and borage – that’s enjoyed all over the state of Hessen and just across some of its borders. Most commonly eaten with boiled potatoes and/or halved hard-boiled eggs, it’s also frequently served with slices of slow-cooked beef (brisket or Picanha/top sirloin cap), thinly sliced cold roast beef, and is very good with a piece of flaky white fish. In the north of Hessen, fewer herbs tend to be used in the sauce and they’re generally chopped coarsely, producing a pale, rough-textured sauce. To the south of the state, the herbs are chopped very finely and the sauce often blended, so it’s smooth, and a brighter shade of green.

Frankfurt’s version of the sauce – Frankfurter Grüne Soße – has been awarded GPI (protected geographical indication) status. It’s made with specific quantities of all seven herbs, which have been grown in city’s southern Oberrad district for generations and are sold in large white paper bundles at local farmers markets. If you’re interested in culinary traditions, you can read more about all of this in my more detailed post about Frankfurter Grüne Soße.

If you don’t have access to the pre-packaged herbs, you can always create your own mix, making up the same 250g weight using some or all of the ones listed above. Don’t be tempted to make any substitutions, and just know that your version isn’t going to taste like Frankfurt’s. The dairy ingredients here are very much down to personal preference and can be adjusted or substituted if necessary: I’ve replaced the yoghurt and sour cream with 250g crème fraîche on more than one occasion, and though I imagine the people of Hessen would want to see me behind bars for it, it tastes absolutely delicious.

Frankfurter Grüne Soße (serves 4)

Ingredients

1 bundle (250g) fresh Grüne Soße herbs
6 tbsp sunflower oil
1 tbsp medium hot mustard
Large pinch of sugar, plus more to taste
2-3 tbsp mild white wine vinegar
3 medium hard-boiled eggs
125g natural yoghurt
125g sour cream or Schmand

Method

Unroll the bundle of herbs and sort through them to remove any dirt or dead leaves. If they need washing, give them a very good shake afterwards and then leave them to try on a tea towel. Chop very finely if you don’t have a blender; if you do, you can chop them a little more roughly as you’ll be making the sauce smooth later.

Put the sunflower oil, mustard, sugar and 2 tbsp of the vinegar into a bowl large enough to hold all the ingredients (including the chopped herbs) and whisk until combined. Peel the eggs and separate the yolks from the whites. Crumble the yolks into the mixture and whisk again till blended (it might be a little lumpy, but it doesn’t matter), then chop the egg whites finely and add those too. Stir it all together, season with salt and pepper, and then fold in the yoghurt and the sour cream or Schmand.

Add to the bowl with herbs and stir to mix. Now give the sauce a quick whizz with a stick blender (or in a standard blender) until your sauce is pale green, fairly smooth and flecked with herbs (see picture above). Check seasoning and add more vinegar to taste – the sauce should be a little bit sharp. If it’s too sharp, add another small pinch of sugar.

Leave your Grüne Soße to sit covered for an hour or so in order to let the flavours develop, then serve at room temperature.

An earlier version of this recipe appeared in The Guardian.