The Recipe at a Glance

This swordfish comes together in one pan in under 20 minutes: a thick steak gets a quick sear, then finishes in a cilantro-mustard butter that melts into the flesh as it cooks. The butter carries bright, sharp flavors without overwhelming the fish. You need a hot skillet, good swordfish steaks cut at least an inch thick, and butter you can brown. The mustard should be Dijon or whole grain — something with body, not yellow ballpark mustard.

The technique matters here because swordfish is dense and can dry out if you rush it. A proper sear locks moisture in, and the butter baste keeps the top from drying while the center finishes. The cilantro goes in at the end so it stays bright and doesn't turn bitter from the heat.

Key Takeaways

  • Swordfish steaks should be at least one inch thick and patted completely dry before they hit the pan, so the surface browns instead of steaming.
  • A hot skillet and a thin layer of oil get the sear; the butter comes in only after the fish has color on both sides.
  • The cilantro-mustard butter is made by whisking Dijon mustard and fresh cilantro into softened butter before cooking, then spooned over the fish as it finishes.
  • The fish is done when it flakes easily at the thickest point and the internal temperature reaches 145°F, which takes 8 to 12 minutes depending on thickness.

Preparing the Swordfish and Seasoning the Butter

Start with swordfish steaks that are between one and one and a half inches thick. Thinner cuts cook too fast and dry out before the butter can do its work. Pat them dry with paper towels — this step is not optional. Moisture on the surface prevents browning and creates steam instead of a crust. Season both sides generously with salt and pepper about 10 minutes before cooking, which gives the salt time to penetrate the flesh.

While the fish sits, make the cilantro-mustard butter. Soften about 4 tablespoons of butter at room temperature — it should be spreadable but still hold its shape. Whisk in 1 to 2 tablespoons of Dijon mustard (start with less if you prefer subtlety), then fold in a small handful of fresh cilantro, finely chopped. Add a pinch of salt. This butter can be made up to a day ahead and kept in the refrigerator; just let it soften slightly before using.

The Sear and the Baste

Heat your skillet over medium-high heat for about 2 minutes. You want it hot enough that a drop of water sizzles immediately. Add a thin layer of neutral oil — vegetable, canola, or light olive oil all work. When the oil shimmers, lay the swordfish steaks in the pan. Do not move them. Let them sit for 3 to 4 minutes until the bottom is golden brown and releases easily from the pan.

Flip the steaks and sear the other side for another 3 to 4 minutes. Once both sides have color, reduce the heat to medium. Place a spoonful of the cilantro-mustard butter on top of each steak. As it melts, tilt the pan and use a spoon to baste the fish with the butter, spooning it over the top repeatedly. This keeps the surface moist and carries the mustard and cilantro flavors into the fish. Continue for 3 to 5 minutes, depending on thickness, until the fish flakes easily when you press it with a fork at the thickest point.

Knowing When the Fish Is Done

Swordfish is firm and dense, so it takes longer to cook than thinner fish. The flesh should be opaque all the way through, with no translucent center. An instant-read thermometer inserted into the thickest part should read 145°F. If you do not have a thermometer, press the fish gently with your finger — it should feel firm but not hard, and a fork should flake the flesh into distinct pieces.

Overcooking swordfish turns it dry and chalky. The butter baste helps prevent this, but watch the clock. A one-inch steak usually takes 8 to 10 minutes total; a thicker steak might need 12. If the top is browning too fast before the center is done, lower the heat further or cover the pan loosely with foil for the last few minutes.

Plating and Serving

Transfer each steak to a warm plate and spoon any remaining butter from the pan over the top. The cilantro will have softened but should still show flecks of green. Serve immediately. This dish does not hold well — the butter will congeal and the fish will continue cooking slightly from residual heat.

Swordfish pairs well with simple sides that do not compete: roasted lemon wedges, steamed green beans, or a small salad of bitter greens dressed with vinegar. If you made extra cilantro-mustard butter, a small dollop on the side lets people add more if they want it.

Why This Method Works for Swordfish

Swordfish has a tight, meaty grain that holds up to high heat better than most fish. The sear creates a protective crust that keeps the interior from drying out, and the butter baste adds fat and flavor without making the dish heavy. The mustard cuts through the richness of the butter and the density of the fish, while the cilantro adds brightness that makes the whole dish feel fresh rather than rich.

This is not a delicate technique — swordfish is forgiving. If you sear it a minute longer than planned, it will not fall apart. If the butter browns a little, that is fine; browned butter adds nuttiness. The main thing is to start with good fish and not walk away from the pan once the basting begins.

Frequently Asked Questions

Can I use frozen swordfish steaks?

Yes, but thaw them completely in the refrigerator first — usually overnight. Frozen steaks release water as they thaw, so pat them extra dry before seasoning. Thawing in the refrigerator rather than at room temperature keeps the texture firmer.

What if I don't have fresh cilantro?

Parsley works, though it is milder. You can also use a small amount of fresh tarragon or skip the herb and add a squeeze of lemon juice to the butter instead. The mustard will still carry the dish.

Can I make this butter ahead and freeze it?

Yes. Form the cilantro-mustard butter into a log, wrap it in parchment, and freeze for up to three months. Slice off what you need and let it soften slightly before cooking. This is useful if you want to keep the butter on hand for other fish or vegetables.

What happens if the butter burns in the pan?

If the butter turns dark brown or black, pour it out and start fresh. Burned butter tastes bitter. If it browns lightly — turning golden and nutty — that is fine and actually adds flavor. The difference is color: light brown is good, dark brown is too far.

How do I know if my swordfish is fresh?

Fresh swordfish should smell like the ocean, not fishy or ammonia-like. The flesh should be firm and pale pink or beige, not gray or brown. Ask your fishmonger when it came in; same-day fish is best. If you are buying frozen, make sure there is no ice buildup or discoloration on the package.