06/19/2013 09:06 am ET Updated Aug 19, 2013

Cooking Off the Cuff: Fish With Dill Pesto

Our main purchases at last Saturday's farmers' market were a plump chicken and a big sack of shelling peas, but those were for Sunday dinner with a friend. For Saturday we needed a more modest hot-weather meal for the two of us, and we rejoiced at the sight of the perfect piece of swordfish: small but thick -- just half a pound, quite enough for two people looking forward to a chicken-and-peas dinner the next day.

The fish would be simply cooked, like a steak, in a skillet, then sliced for service; the question was what to serve with it. I love variations on Italian-style pesto and salsa verde with fish; these herb sauces know no season but can easily be adapted to market finds. And among our other finds on Saturday were a bunch of fragrant dill and a basket of one-inch tomatoes, both from a favorite vendor, Stokes Farm. It is early for tomatoes, but these were savory and sweet and juicy.

I quickly decided that the green sauce would be a one-herb version: pure dill, which has an affinity for fish and is something Jackie and I love in any form. I thought I'd use an immersion blender to puree it with olive oil, add some lemon zest and juice, then stir in some cut-up tomatoes at the last minute. When I got home and made the basic puree (using half the bunch of dill, mostly stemmed, the grated zest of a medium lemon, the juice of less than half the same lemon, salt and a quarter cup of olive oil), I found it a little flat. More lemon? No, it was quite lemony already. So I went back to the mixture's salsa verde roots and added a teaspoon of capers, rinsed and squeezed dry, and one cornichon, roughly chopped. Once these had been beaten up by the blender, they rectified the flaw perfectly.

I cooked the fish in a skillet slicked with olive oil, turning it every minute over medium-low heat, rising to medium at the end, until it was golden brown and cooked but still very juicy. While it rested (for just a few minutes), I cut three (or was it four?) little tomatoes into eight wedges each and stirred these into the dill pesto. I sliced the fish and served it drizzled with its own juices and with sauce on the side, plus the rest in a bowl on the table (it all got eaten, every drop). Couscous with fennel and lemon was the accompaniment -- surprisingly apt considering it was left over from a few days before.

I'd worried, a little, that the capers and cornichon would be unfair competition for the dill, but the herb was the unquestionable star, along with the tomatoes, which made the sauce juicier and provided big points of sweet, savory flavor. (The same sauce, but less of it, would make a fine dressing for a tomato salad, in fact.)

Apart from something really fragile in flavor and texture -- such as the smaller, milder flatfish we find in our East Coast waters -- I can't think of a fin-fish that wouldn't work well with this dill-tomato pesto/salsa verde, so file it away under "Fish, misc."

Swordfish (Or Any Fish) With Dill Pesto