This is my Sunday go-to dinner. I learned it in 1995 from a woman nicknamed Titi. She was from Genoa and married to Giorgio Gallizio, the man who hired me to open Giorgio's at the Pier in Juneau, Alaska. Giorgio wanted his wife to put some of her dishes on the menu. I was skeptical at first, but then she started cooking for me. Skepticism be gone! She made me some incredible dishes, like ravioli Genovese (sweetbread and brain ravioli), fried porcini mushrooms, and halibut with peas. The halibut was my favorite, and it went on the menu at Giorgio's. It was on my menu at Vetri for a while, too, but nowadays it shows up more often on my own kitchen table. My wife just loves it. Sometimes, I'll toss in a little chopped pancetta to make it richer. But don't even bother using anything but freshly shelled peas. The smaller, the better. Once they get too big, they go from sweet to starchy.
Heat the oil in a large skillet over medium heat and sauté the peas, shallot, and garlic until soft but not browned, 3-4 minutes. Add the wine, red pepper flakes, and ½ cup water and simmer rapidly over medium-high heat until only a few tablespoons of liquid are left in the pan, 5-6 minutes.
Cut the halibut into 6 pieces and season all over with salt and pepper, to taste. Add the halibut to the pan and drizzle in the sherry vinegar. Reduce the heat to medium and cook, turning a few times, until you can almost break the halibut apart with your fingers, 6-8 minutes, adding the parsley halfway through and spooning the liquid from the pan over the fish now and then. Transfer the fish to a platter or plates and keep warm.
Increase the heat to medium-high and add another ½ cup water in 2-tablespoon increments, stirring during each addition. Cook until the liquid in the pan reduces in volume and thickens slightly and the peas are tender, 6-8 minutes total. Season with salt and pepper, to taste. Remove the garlic and pour the peas and sauce over and around the fish on the platter or plates.