Portion and dry the fish: Divide the 640 g Arctic char into four 160 g portions (if not already portioned). Pat skin and flesh very dry with paper towels. Dry fish sears — moisture prevents browning and encourages steaming, so removing surface moisture ensures a deep, even crust on the skin.

Score the skin (optional) and season: Lightly score the skin with 2–3 shallow slashes (don’t cut the flesh) to stop the fillet from curling as it cooks. Season both sides with a light sprinkle of kosher salt and white pepper. Scoring keeps the fillet flat against the pan so the skin crisps evenly.

Zest and juice the oranges: Zest two of the oranges (you want about 2–2½ tsp total zest) and set aside. Halve all four oranges; juice two halves (one per two servings) to yield roughly 60–80 ml (about 1/4 cup) of fresh orange juice total — we use the rest of the orange halves as a garnish or segment them for the plate. Fresh juice brightens the sauce and raw zest adds concentrated citrus oils for fragrance.

Make the citrus-ginger base: In a small bowl combine the orange juice, 4 g (2 tsp) of the grated ginger and 10 ml (2 tsp) tamari. This is the searing glaze — the acid and salt will deglaze and flavor the pan, and ginger brings warmth and aromatic heat.

Prepare the greens: Roughly chop the bok choy and chard (if stems are large, separate stems from leaves). Heat a wide skillet over medium-high heat, add the toasted sesame oil (20 ml) and immediately add the chopped stems first. Sauté 1–2 minutes to soften stems, then add the leaves, 4 g (about 1 tsp) grated ginger, and 10 ml (2 tsp) tamari. Toss until just wilted, 1–2 minutes more — quick, high heat cooking preserves vibrant color and bright flavor. Season with a pinch of salt and white pepper, remove to a warm plate and keep warm.

Heat the searing pan and oil: Use a heavy-bottomed nonstick or stainless steel skillet; heat it over medium-high until hot but not smoking. Add the neutral high-heat oil (15 ml) and swirl to coat. A properly heated pan gives an instant sizzle and promotes Maillard browning — that golden-brown crust is flavor.

Sear the fish, skin-side down: Place fillets skin-side down in the hot pan and press gently for 10–15 seconds with a spatula to ensure full contact. Cook skin-side down for 3½–4½ minutes (depending on thickness) without moving — this creates a crisp, golden skin and cooks the fish most of the way through while protecting the delicate flesh.

Flip and finish with citrus-ginger glaze: Carefully flip each fillet and reduce heat to medium. Add the orange-ginger-tamari mixture to the pan and let it bubble for 20–30 seconds to slightly reduce — the sauce is both a finishing glaze and a gentle deglazer. Add the butter (14 g) and spoon the melted butter and reduced glaze over the fish for 30–45 seconds; this emulsifies the sauce and gives it a glossy finish while adding richness.

Check for doneness and rest briefly: Cook another 30–60 seconds after glazing until the fish reaches your desired doneness (internal temp 50–52°C / 122–126°F for medium-rare, or 55°C / 131°F for medium). Rest 2 minutes on a warm plate — resting lets residual heat finish cooking and the juices redistribute so each bite is moist.

Plate: Spoon a nest of warm sesame greens onto each plate. Place the seared char on top (skin-side up to keep it crisp). Spoon any remaining orange-ginger pan sauce over the fish and finish with reserved orange zest, sliced scallions and optional orange segments for brightness. A final sprinkle of white pepper lifts the citrus and adds subtle heat.

Serve immediately: The contrast between hot glazed fish, crisp skin and warm sesame greens is best enjoyed right away.