Quick Swordfish with Leftover Lacto-Plum Sauce & Avocado-Radish Salad

If you caught my previous post on duck breast, you might remember the batch of homemade lacto-fermented plums I turned into a bright, acidic reduction. I had a good amount of that sauce left in the fridge and wanted to use it for a quick, low-effort weeknight meal around it.

I picked up a swordfish fillet at the supermarket, but with almost 500gr the cut ended up being way chunkier than expected. Since there was plenty of protein on the plate, I decided to skip the usual starchy side (no potatoes or rice tonight) and keep things light with a fresh, crisp salad.

Ingredients (2 Servings)

The Swordfish & Brine

• 400–450 g Swordfish Fillet (skin and dark lateral muscle trimmed)
• 300 mL Water + 30 g Fine Sea Salt (for a quick 10% brine)
• 15 g Cold Butter (plus a splash of neutral oil for searing)

The Reconstituted Lacto-Plum Sauce

• 100–150 mL Leftover Lacto-Plum Reduction
• 15–30 mL Light Stock or Fresh Lemon Juice (to thin it out)

The Avocado & Radish Salad

• 100 g Mixed Salad Greens (butter lettuce, chervil, or crisp leaves)
• 1 Medium Avocado (pitted and sliced)
• 4–5 Red Radishes (sliced paper-thin)
• 15 mL (1 tbsp) Extra Virgin Olive Oil
• 7.5 mL (1/2 tbsp) Fresh Lemon Juice
• Flaky sea salt to taste

Step-by-Step Instructions

Step 1: Brine the Fish & Ice the Radishes (20 Minutes)

1. Brine the Swordfish: Dissolve the salt in the water to make a 10% brine. Submerge your trimmed swordfish for exactly 20 minutes at room temperature. Why do this? Brining binds moisture inside the fish and prevents that unsightly white protein (albumin) from leaking out while you sear.
2. Ice the Radishes: Shave the radishes paper-thin using a mandoline and drop them into a bowl of ice water for 15 minutes. This locks in maximum water pressure so they stay super crisp.

Step 2: Sear the Fish & Reheat the Sauce (8 Minutes)

1. Dry Thoroughly: Remove the swordfish from the brine and dry it aggressively with paper towels.
2. High-Heat Sear: Heat a heavy skillet over medium-high with a tiny bit of high-heat oil until shimmering. Lay down the swordfish and let it sear untouched for 2 to 3 minutes until a rich golden-brown crust forms.
3. Flip & Baste: Flip the steak over, drop 15 g of cold butter into the pan, and lower the heat slightly. Spoon the foaming butter over the fish for 1.5 to 2 minutes. Pull it from the pan when the center hits 52 °C and let it rest on a warm plate for 3 minutes.
4. Loosen the Sauce: Warm your leftover lacto-plum reduction in a small pan over very low heat. Whisk in a splash of stock or fresh lemon juice to loosen the texture back into a silky spoonable sauce.

Step 3: Toss and Plate

1. Toss the Salad: Spin or pat your iced radishes dry. In a bowl, toss the greens, radishes, and sliced avocado with the olive oil first. Once everything is coated, season with fresh lemon juice and flaky sea salt right before serving.
2. Plate Up: Place the rested swordfish on the plate, pile the avocado-radish salad right alongside, and spoon the warm lacto-plum sauce around the fish.

Troubleshooting Quick-Fixes

How do I stop swordfish from drying out? Swordfish gets tough fast if it overheats past 54 °C. Always pull the fish off the heat right around 50–52 °C as residual carryover heat will gently bring it to the ideal internal temperature while it rests.

Why coat the salad with oil before the lemon/salt? If you add salt or acid directly to delicate leaves, they draw moisture out of the plant cells and make the salad soggy. Coating the greens with olive oil first creates a light waterproof shield that keeps everything crisp on the plate.