Grüne Soße Festival (Green Sauce Festival)

Grüne Soße is Frankfurt's most local dish: a cold, thick sauce of seven fresh herbs bound with sour cream or yogurt, poured over boiled potatoes and hard-boiled eggs. It sounds modest and it is fiercely defended. Every May the Roßmarkt square hosts a week-long competition to find the best one, with live music, a food mile and a jury that has to eat green sauce every single night.

Which seven herbs? That is the argument. Depending on the cook and the household, the mix draws on tarragon, parsley, chives, dill, cress, basil, lovage, chervil, sage and lemon balm, finished with butter, nutmeg, salt, pepper, lemon juice and hot milk. Nobody agrees, which is exactly why a competition makes sense.

There is a persistent legend that green sauce was Goethe's favorite dish, invented by his mother, Frau Aja. She almost certainly did not invent it. She mentions finding the recipe in her grandmother's cookbook. Goethe's documented favorites ran to Teltow turnips, artichokes, game, warm cabbage salad with bacon and head cheese. Scholars think the sauce arrived in Frankfurt around 1850, well after both of them, first recorded as a spring dish, because that is when the first fresh herbs reached the market.

The format is straightforward. Forty-nine cooks or teams compete across seven days, and each evening a jury picks a daily winner. Before the verdict, the 650 guests in the festival tent taste the sauces, served the traditional way with potatoes and eggs. At the end of the week the daily winners face off in a final, and the audience in the tent votes for the overall champion.

Outside the tent, a culinary mile of 24 stalls runs from the Roßmarkt to the Hauptwache with food from around the world, plus green sauce in inventive forms: a croissant baked crisp with the sauce inside, asparagus salad in an herb dressing, a couscous salad with an oriental take built on mint, cilantro, chili and yogurt, and Italian ice cream made with the green sauce herbs. On the weekend there is live music and a raffle for charity.

If you want to try making it at home, the oldest recipes are the simplest. One from 1856 calls for a hard-boiled egg yolk stirred with two tablespoons of fine salad oil, several spoons of mustard, then finely chopped herbs including tarragon, chervil, chives, salad burnet, parsley and borage, finished with a little vinegar, salt and pepper, served with boiled potatoes. The trick is patience: that version gets stirred for a good 15 minutes to reach the right consistency.