The Whole Tuna Recipe

Prepare potatoes

Using a box grater or food processor, coarsely grate the peeled yellow potatoes. Place grated potatoes into a clean kitchen towel or cheesecloth and squeeze out as much moisture as possible into a bowl (reserve the starch that settles for later use if desired). Transfer drained grated potato to a large bowl. If using a small amount of frozen shredded potato for extra crispness, fold it in now.

Season potatoes

Add 1 tsp salt, 1/2 tsp black pepper, and garlic powder to the grated potatoes. Mix thoroughly so the seasonings distribute evenly.

Form and pan-fry rosti

Heat 2 tbs neutral oil and 1 tbs butter in a large nonstick or cast-iron skillet over medium-high heat until shimmering. Press half of the grated potato into a compact round (about 7–8 inches) in the pan, roughly 1–1.5 cm thick. Cook undisturbed for 6–8 minutes until the underside is deeply golden and crisp. Carefully flip (using a plate to assist if needed), add another 1 tbs oil and 1 tbs butter around edges, and cook the second side for 5–7 minutes until crisp and cooked through. Remove to a warm oven (120°C / 250°F) to keep warm while you cook the tuna. Repeat with remaining potato to make a second rosti (or make smaller individual rosti if preferred). Taste and adjust with a pinch of salt if needed.

Prepare tuna belly

Pat the tuna belly dry again. Season both sides with the remaining 1 tsp salt and remaining 1/2 tsp black pepper. Let rest at room temperature for 5 minutes. The belly is rich and fatty — keep pieces intact if possible.

Sear tuna belly

Heat a clean skillet over high heat until smoking point, then add 1 tbs neutral oil. Place the tuna belly, flesh side down, and sear for 45–60 seconds undisturbed to develop a dark caramelized crust. Flip and sear the other side for 30–45 seconds for rare to medium-rare (adjust time by thickness). During the last 15 seconds, add a small knob of butter and baste the top to add gloss and flavor. Remove tuna and let rest 2–3 minutes. For a slightly more cooked center, sear an extra 15–30 seconds per side.

Slice and assemble

Slice the tuna belly into 1–1.5 cm thick medallions. Place a rosti on each plate, arrange 3–4 tuna medallions atop the rosti. Spoon a few small dollops of horseradish cream (from next section) around the fish, scatter finely sliced chives and microgreens, and finish with a light drizzle of extra virgin olive oil and a dusting of smoked paprika or Aleppo pepper if using. Serve with lemon wedges on the side.

Make horseradish cream

In a bowl, whisk together the prepared horseradish, sour cream, milk (or buttermilk), Dijon mustard, lemon juice, 1/2 tsp sea salt and 1/4 tsp black pepper until smooth and slightly loose in consistency. Taste and adjust heat with more horseradish if desired. Chill for at least 10 minutes to let flavors mingle.

Final garnishes

Just before serving, taste the horseradish cream again and adjust seasoning. Finely slice the chives and scatter over the plated dish. Toss microgreens or baby arugula lightly with a pinch of salt and a few drops of lemon if using, then place a small handful beside the rosti for freshness.

Serve immediately so the rosti stays crisp and the tuna remains warm and tender. Provide lemon wedges for diners to squeeze over the tuna. Estimated plating: place 1 rosti and 3–4 tuna medallions per serving, with 1–2 tbs horseradish cream and a small handful of greens.