Grilled Fish with Salmoriglio

From the garden

• ⅓ cup fresh oregano (thyme, or half of each, works too), leaves stripped and finely chopped
• 1½ lb small waxy potatoes, halved
• 2 cloves garlic, minced to a paste with a pinch of salt

From the pantry

• 1½ lb firm white fish steaks (swordfish is traditional; halibut or cod work)
• 2 lemons, one juiced, one halved for the grill
• ½ cup olive oil · grassy, peppery oil; it is half the sauce
• salt · to taste
• black pepper

1. Boil the potatoes in well-salted water until a knife slides through without resistance, 15–18 minutes. Drain and keep them warm in the pot: they will take up whatever sauce runs off the fish.
2. Whisk the oregano, garlic, and lemon juice with a good pinch of salt and plenty of pepper while the potatoes cook. Beat in the olive oil slowly, in a thin stream, until the sauce looks cloudy.
3. Loosen the salmoriglio with 2 tablespoons of hot water and keep whisking for a few seconds. Warm water is what turns it from a slick of oil into a sauce that clings.
4. Heat a grill or ridged pan until a drop of water skitters. Oil and season the fish, lay the lemon halves cut-side down alongside, and cook the fish 3–4 minutes a side, until barely firm in the middle.
5. Spoon half the salmoriglio over the fish and rest it 5 minutes so the herb steeps into the warm flesh. Dress the potatoes with the rest and serve with the grilled lemon for squeezing.