Another sauce for grilled mullet: rue, mint, coriander, fennel, all of them green; pepper, lovage, honey, liquamen, and a little oil (and vinegar). APICIUS 10.1.12.
The idea of a ‘green sauce’ made from large quantities of different fresh herbs with a simple acid/oil combo and minimal spices goes back centuries and can be found in all areas of the Mediterranean. The historical links are quite distinct in the case of salsa verde. We can see the basic idea in Apicius above, and we find a very similar recipe from the writer Columella from the early Roman Empire as a basic sauce for dipping. We find the same ideas in early medieval cooking in France, Italy, and Spain, though a single herb is usually recommended. A green sauce in 14th century France, ‘sauce vert’, found in the cookbook known as the Viandier, was made with breadcrumbs, parsley, ginger, vinegar, lemon juice, and wine, and was often served with fish, as ours will be. The modern Italian version maintains the idea of a single herb, parsley, with vinegar, capers, garlic, onion, anchovies, olive oil, and mustard. The anchovies hint at a strong association with the Roman original. The Spanish idea of a green sauce is strongly associated with fish too as they were always cooked together. The Pan-American idea of green sauce has evolved to include green tomatoes and chilli in Mexico, but we need not go there.
I have embraced the Roman idea of multiple varieties of herbs and also taken garlic from the Italian version and added vinegar. The Apicius recipe suggests that this sauce should be served with mullet, and this is entirely delicious. I used sea bass for my trial, but a fish with a firm flesh is ideal. The fish sauce needs to be quite punchy, so I am using an aged colatura, or you could use flor di garum or Red Boat.