Swordfish with Sweet and Hot Pepper Sauté

Remove the swordfish steaks from the refrigerator 15 minutes before cooking. Pat each steak thoroughly dry on both sides with paper towels; surface dryness is essential for a deep golden crust rather than steam. Season generously on both sides with 3g of the kosher salt and 1g of the black pepper. Set the steaks aside at room temperature to temper while you prepare the vegetables.

While the swordfish tempers, prepare the vegetables. Core and seed the red and yellow bell peppers, then slice into 1cm (about 1/2 inch) strips. Halve the onion from root to tip and slice into thin half-moons. Mince the garlic. Halve the jalapeño lengthwise, scrape out the seeds and white ribs for moderate heat (leave some seeds in for spicier results), then mince. Zest the lemon with a microplane, halve it, and juice. Chop the parsley leaves. Group everything within easy reach of the stove.

Heat 20ml of the olive oil in a 30cm cast iron or heavy-bottomed skillet over medium-high heat until the oil shimmers and just begins to send up thin wisps of smoke, about 2 to 3 minutes. Carefully lay the swordfish steaks in the oil, leaving at least 2cm of space between each piece. Sear undisturbed for 4 minutes, until a deep golden-brown crust forms on the bottom and the steak moves freely when nudged with the spatula.

Flip each steak using the fish spatula or tongs. Reduce the heat to medium and cook the second side for 3 to 4 minutes, until an instant-read thermometer inserted into the thickest part reads 60 to 61°C (140 to 142°F). The edges should look opaque while the very center still feels slightly yielding when pressed; carryover cooking will bring the fish safely to 63°C (145°F) during the rest.

Transfer the swordfish steaks to a warm plate and tent loosely with aluminum foil. Let rest for 5 minutes while you prepare the pepper sauté; this allows the juices to redistribute and the internal temperature to climb gently to 63°C (145°F) at the thickest part. Do not skip this rest, as cutting in immediately will cause the juices to run out onto the plate.

Return the same skillet to medium heat (no need to wipe it out; the browned bits left from the fish add flavor). Add the remaining 10ml of olive oil and the sliced onion. Sauté for 4 to 5 minutes, stirring frequently, until the onion softens, turns translucent, and develops lightly golden edges.

Add the sliced red and yellow bell peppers along with a small pinch of salt. Increase the heat to medium-high and cook for 8 to 10 minutes, stirring every couple of minutes, until the peppers are tender with charred edges and any liquid pooled in the pan has mostly evaporated. The peppers should look glossy and slightly collapsed rather than crisp and watery.

Reduce the heat to medium-low. Add the minced garlic and jalapeño and cook for 60 to 90 seconds, stirring constantly, until fragrant but not browned. Garlic burns quickly, so move the pan off the heat entirely if you notice any browning.

Add the lemon juice and use a wooden spoon to scrape up any browned bits from the bottom of the pan. Let the juice bubble and reduce by half, about 30 to 45 seconds. Remove the pan from the heat and add the cold butter cubes, swirling continuously until they melt into a silky, emulsified sauce. Stir in the lemon zest and taste; adjust with a pinch of the remaining kosher salt if needed.

Spoon a generous bed of the pepper mixture onto each of four warmed plates. Lay a rested swordfish steak on top of the peppers. Spoon the lemon-butter pan sauce over and around the fish. Scatter the chopped parsley across the top and finish with a final grind of the remaining black pepper. Serve immediately with lemon wedges on the side and crusty bread if desired.