What garlic mustard pesto does to fresh tuna
Garlic mustard pesto turns tuna into something bright and sharp—the mustard greens bring a peppery bite that cuts through the fish's richness, while garlic and oil carry that flavor deep into the flesh. The pesto works best on tuna that is either seared rare or gently poached, where the fish stays tender enough to absorb the sauce without falling apart. A thick sear on the outside, rare inside, then topped with a spoonful of pesto while the fish is still warm: that is the move.
Garlic mustard grows wild in spring across much of North America, and if you fish inland streams or keep a garden, you likely have it nearby. The whole plant is edible—leaves, stems, and seed pods—and it tastes like a cross between arugula and horseradish. Fresh from the water or the garden, it makes a pesto that tastes nothing like the basil version. It is sharper, more mineral, and it does not fade.
Key Takeaways
- Garlic mustard pesto pairs best with seared tuna that is rare in the center, where the fish stays tender enough to absorb the sauce.
- You can harvest garlic mustard from the wild in spring, or buy it at farmers markets; the leaves, stems, and seed pods are all usable.
- The pesto keeps for three days in the refrigerator and freezes well for up to two months, so you can make it in bulk when garlic mustard is abundant.
- A single tablespoon of pesto per serving is enough; the flavor is concentrated and the fish should remain the star of the plate.
Harvesting and preparing garlic mustard
Garlic mustard grows as a rosette close to the ground in its first year, then sends up a flowering stalk in spring of the second year. The leaves are heart-shaped and deeply toothed, and they smell distinctly garlicky when you crush them. Pick the young leaves and tender stems in April and May, before the plant flowers; after flowering, the leaves become tough and bitter. Wear gloves if you have sensitive skin—the plant can cause a mild rash in some people.
Rinse the leaves and stems well under cold water and spin them dry. Remove any thick stem bases and discard yellowed or damaged leaves. The tender upper leaves and the thin stems are what you want. If you find seed pods—small, thin, four-sided capsules that appear after flowering—save those too; they have a sharp, almost wasabi-like heat and add complexity to the pesto.
Making the pesto
Combine two cups of packed garlic mustard leaves and stems, one-quarter cup of raw garlic cloves (about four large cloves), one-half cup of good olive oil, two tablespoons of lemon juice, one tablespoon of Dijon mustard, and one-half teaspoon of salt in a food processor. Pulse until the mixture is roughly chopped but still has texture—you want flecks of green visible, not a smooth paste. Taste and adjust salt and lemon juice. If you have seed pods, add one tablespoon of them at the end and pulse once or twice to keep them slightly chunky.
The pesto will be looser than basil pesto because garlic mustard has less oil in its leaves. That is correct. If it seems too thin, add another tablespoon of olive oil. If it tastes too sharp, add a squeeze more lemon juice to round out the edges. The pesto keeps in a glass jar in the refrigerator for three days, or frozen in ice cube trays for up to two months; thaw it at room temperature before serving.
Searing tuna for the pesto
Use a thick tuna steak—at least one and one-half inches thick—cut from the loin. Pat it completely dry with paper towels; any moisture on the surface will steam the fish instead of searing it. Season both sides generously with salt and pepper about ten minutes before cooking, which gives the salt time to penetrate the flesh.
Heat a cast-iron or stainless steel skillet over high heat until it is smoking. Add a thin film of neutral oil with a high smoke point—grapeseed, avocado, or refined peanut oil all work. Lay the tuna in the pan and do not move it. Sear for ninety seconds on the first side, then flip and sear for ninety seconds on the second side. The outside should be deeply browned and crispy. Remove the fish to a cutting board and let it rest for two minutes. The center will be rare to medium-rare, which is where the pesto can do its work.
Plating and serving
Slice the tuna into half-inch-thick pieces and arrange them on a warm plate. Spoon one tablespoon of pesto over the top, or serve it on the side for people to add as they like. The pesto will warm slightly from the heat of the fish and release its oils. A squeeze of fresh lemon juice over everything ties it together.
Serve with something simple: crusty bread to soak up the pesto, a salad of tender spring greens, or roasted new potatoes. The pesto is bold enough that it does not need competition on the plate. If you are cooking for a group, make extra pesto; people will want more than they think they will.
Storing and using leftover pesto
Garlic mustard pesto keeps longer than basil pesto because the raw garlic acts as a preservative. Store it in a glass jar with a thin layer of olive oil on top to keep air off the surface. It will last three days in the refrigerator. To freeze it, spoon the pesto into ice cube trays, freeze solid, then pop the cubes into a freezer bag. Each cube is roughly one tablespoon, which is the right amount for one serving of fish.
Beyond tuna, the pesto works on any firm white fish, on grilled chicken, or stirred into mayonnaise for sandwiches. It is also good on roasted vegetables or swirled into soup. If you find yourself with more garlic mustard than you can use fresh, making pesto is the best way to preserve the flavor for later in the year.
Frequently Asked Questions
Can I use store-bought garlic mustard instead of wild?
Yes. Farmers markets often sell garlic mustard in spring, especially in regions where it grows wild. The flavor is the same, and you skip the foraging step. If you cannot find it fresh, you can substitute arugula mixed with a small amount of fresh horseradish, though the result will be milder.
What if my tuna is thinner than one and a half inches?
Reduce the searing time to sixty seconds per side. Thinner steaks cook through faster and are harder to keep rare in the center. If your fish is less than one inch thick, it is better poached gently in simmering water for four to five minutes, then topped with pesto after cooking.
Does the pesto work on canned tuna?
It can, but the texture and flavor of canned tuna is so different from fresh that the pesto becomes the whole dish rather than an accent. If you want to use it, drain the canned tuna well, mix it gently with the pesto, and serve on toast or crackers.
How do I know if garlic mustard is safe to eat?
Garlic mustard is not toxic, but make sure you have the right plant. The leaves should smell distinctly garlicky when crushed, and the plant should have heart-shaped, toothed leaves. If you are uncertain, bring a sample to a local extension office or an experienced forager before eating it.
Can I make this pesto without a food processor?
Yes. Chop the garlic mustard leaves and garlic very finely by hand, then mash them together in a mortar and pestle with the salt. Stir in the oil, lemon juice, and mustard by hand. The texture will be slightly chunkier, which is fine—some people prefer it that way.