From "Le Viandier," the Recipe Book of Guillaume Tirel, head chef to Philip VI of France:
Bright Green Soup of Eels:
Skin or scald them, and cook them in wine and water.
Crush bread and parsley, with just a bit of saffron in the greens (to make it bright green), and soak in your broth.
Crush ginger steeped in verjuice, and boil everything together.
You can add good cheese cut into little cubes if you wish.
Ah, nothing like a good dish of Middle Ages stew. More to follow...
Verjuice is an acidic juice that you get from crushing unripe grapes or other sour fruit. These days, cooks use tart wines or vinegars instead.
And we know that this was a recipe for royalty, because ginger was fabulously expensive in Medieval Europe (pre-Crusades, a pound of ginger was worth a sheep). Saffron wasn't too cheap, either.
Let me know what happens if you try this at home.
I hereby disclaim any responsibility.