The Recipe at a Glance
Swordfish's firm, meaty texture stands up beautifully to bold flavors, and this combination of lemon, garlic, and mustard does exactly that without overwhelming the fish itself. You sear thick steaks in a hot pan, then finish them with a quick pan sauce made from Dijon mustard, fresh lemon juice, minced garlic, and a little butter. The whole dish takes about 15 minutes from start to finish, and the sauce clings to the fish rather than pooling underneath it.
The key is using steaks cut at least an inch thick—thinner cuts dry out before the exterior gets a proper crust. A cast-iron or stainless steel pan gives you the heat retention you need for that crust. Nonstick pans work, but they don't brown as aggressively, and browning is where the flavor lives.
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 cast-iron or stainless steel pan sears the fish properly in about three to four minutes per side, depending on thickness.
- The mustard-lemon-garlic sauce comes together in the same pan after the fish is done, using the browned bits stuck to the bottom for depth.
- Swordfish is done when it flakes easily at the thickest part and has turned from translucent to opaque white, not when it falls apart.
Choosing and Preparing Your Swordfish
Buy swordfish steaks that are uniform in thickness—ideally one and a quarter inches. If your fishmonger cuts them thinner, ask them to cut thicker steaks instead, or buy a larger piece and cut it yourself at home. Uneven thickness means the thin parts overcook while the thick parts are still raw in the middle.
Pat the steaks dry with paper towels at least 10 minutes before cooking. Moisture on the surface prevents browning and creates steam, which is the opposite of what you want. If you have time, salt them lightly on both sides and let them sit uncovered in the refrigerator for 30 minutes to an hour. This draws out surface moisture and seasons the flesh evenly.
Remove the steaks from the refrigerator 10 minutes before cooking so they're not cold when they hit the pan. A cold fish takes longer to cook through, and by the time the center is done, the outside is overdone.
Searing the Fish in the Pan
Heat your cast-iron or stainless steel pan over medium-high heat for at least three minutes. You want it hot enough that a drop of water sizzles and evaporates immediately. Add a thin film of oil with a high smoke point—grapeseed, avocado, or refined vegetable oil all work. Olive oil burns at this temperature and will taste bitter.
Place the swordfish steaks in the pan without moving them. Resist the urge to poke, flip, or shift them around. Let them sit for three to four minutes until the bottom is golden brown and releases easily from the pan. Flip once and cook the other side for another three to four minutes. The exact time depends on thickness and your stove's heat output, but aim for an internal temperature of 140°F at the thickest part.
Transfer the cooked steaks to a warm plate and tent loosely with foil while you make the sauce. They'll continue cooking slightly as they rest, and the foil keeps them warm without trapping steam that would soften the crust.
Building the Mustard-Lemon-Garlic Sauce
Keep the pan on the heat. You'll see browned bits stuck to the bottom—that's flavor, and you're going to use it. Add two minced garlic cloves and cook for about 30 seconds, stirring constantly, until fragrant. Don't let the garlic brown or it turns bitter.
Pour in a quarter cup of dry white wine or chicken stock, scraping the bottom of the pan with a wooden spoon to loosen all those browned bits. Let it simmer for one minute. Add two tablespoons of Dijon mustard and the juice of one lemon, stirring until smooth. Taste it—the mustard should be noticeable but not harsh, and the lemon should brighten the whole thing without making it sour.
Remove from heat and stir in one tablespoon of cold butter, cut into small pieces. The butter emulsifies into the sauce, making it silky and rich. If the sauce is too thick, add a splash more stock or water. If it's too thin, let it simmer for another 30 seconds. Pour the sauce over the swordfish steaks and serve immediately.
Timing and Temperature Guide
| Steak Thickness | Sear Time Per Side | Internal Temperature | Doneness |
|---|---|---|---|
| 1 inch | 3 to 3.5 minutes | 135°F to 140°F | Moist, flakes easily |
| 1.25 inches | 3.5 to 4 minutes | 140°F to 145°F | Opaque throughout, still tender |
| 1.5 inches | 4 to 5 minutes | 145°F | Firm, no translucence |
Use an instant-read thermometer inserted horizontally into the thickest part of the steak, away from any bones. Swordfish continues to cook as it rests, so pull it from the pan a few degrees before your target temperature. If you don't have a thermometer, look for the flesh to turn from translucent to opaque white and flake easily when you press it with a fork.
What to Serve Alongside
Swordfish is substantial enough to carry a meal on its own, but it pairs well with simple sides that don't compete with the lemon-mustard sauce. Roasted asparagus, green beans, or broccoli all work—just toss them with olive oil, salt, and pepper, and roast at 425°F while the fish cooks. A small salad of bitter greens dressed with lemon vinaigrette echoes the sauce without repeating it.
If you want starch, try crusty bread to soak up the sauce, or boiled new potatoes dressed with a little butter and fresh parsley. Avoid heavy starches like rice or pasta, which will make the plate feel sluggish. The sauce is the star here, and you want room to taste it.
Common Mistakes and How to Avoid Them
The most common mistake is cooking swordfish too long. It's a lean fish with very little fat, so overcooking makes it dry and tough. If you're nervous about doneness, use a thermometer—140°F is the sweet spot. The fish will be opaque and flake easily, but still moist inside.
The second mistake is not getting the pan hot enough. If the pan isn't hot when the fish hits it, the surface steams instead of browning, and you lose the crust that holds the sauce. Test the pan with a drop of water before you add oil. It should sizzle aggressively.
The third mistake is moving the fish around in the pan. Every time you flip or shift it, you interrupt the browning process and risk tearing the delicate surface. Sear it undisturbed on one side, flip once, and leave it alone.
Frequently Asked Questions
Can I use frozen swordfish steaks?
Yes, but thaw them completely in the refrigerator overnight before cooking. Frozen fish releases water as it thaws, and if you cook it while still partially frozen, that water will steam the surface and prevent browning. Pat them extra dry before they go in the pan.
What if I don't have Dijon mustard?
Whole grain mustard works well and adds texture. Yellow mustard is milder and less interesting. If you have neither, skip the mustard and add an extra tablespoon of butter and a pinch of salt to the lemon-garlic sauce instead. It won't be the same dish, but it will still be good.
Can I make this sauce ahead of time?
No—the sauce needs to be made in the pan while it's still hot, so the butter emulsifies properly and the flavors are bright. You can prep the ingredients (mince the garlic, juice the lemon, measure the mustard) ahead of time, but make the sauce itself right after the fish comes out of the pan.
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 spring back when you press it gently. Avoid steaks that look dull or have a grayish tint—they should be bright pink or tan. Buy from a fishmonger who can tell you when the fish arrived.
What wine should I use in the sauce?
Any dry white wine works—Sauvignon Blanc, Pinot Grigio, or even a basic house white. Avoid oaky wines like Chardonnay, which can overpower the delicate sauce. If you don't have wine, use chicken or vegetable stock instead. The sauce will be less complex but still delicious.