Preheat and prep: Preheat your oven to 425°F (220°C). A hot oven helps the vegetables caramelize quickly and the fish to cook through fast without drying. Line a rimmed baking sheet with parchment or foil for easy cleanup.

Prepare the sweet potatoes: Place 800 g peeled & cubed sweet potatoes in a pot and cover with cold water (starting them in cold water ensures even cooking). Add a pinch of salt and bring to a boil over high heat, then reduce to a simmer until fork-tender, 12–15 minutes. Cooking them until just tender makes the mash silky rather than gluey.

Season & roast the Brussels sprouts: While the potatoes cook, toss 480 g halved Brussels sprouts with 1 tbsp (15 ml) of the olive oil (we'll use the 20 ml total but reserve a small amount for the mash), a light pinch of salt and pepper. Spread cut-side down on one half of the prepared baking sheet—you want the cut surface against the metal to encourage browning. Roast in the preheated oven for 18–22 minutes until deeply golden at the edges and tender inside. Turn once if you want even color. Roasting develops the sprouts’ natural sugars and creates crisp edges that contrast the soft mash.

Toast the sesame seeds: After putting sprouts in the oven, warm a small dry skillet over medium heat and toast 6 g sesame seeds for 1–2 minutes, shaking the pan constantly until fragrant and lightly golden. Toasting blooms their nutty aroma and gives a brighter sesame flavor; set aside for finishing the sprouts.

Make the miso-citrus glaze: In a small bowl, whisk together 20 g white miso paste with 60 ml water until smooth (this thins the miso so it spreads and glosses the fish rather than clumping). Stir in the zest of 1 orange (reserve a little zest for the mash if you like — aim to divide zest roughly 1/2 + 1/2), and 10 ml low-sodium soy sauce. Taste: the glaze should be umami-forward with a bright citrus lift; a touch more soy can add saltiness, but go lightly because miso is already salty.

Prepare the cod: Pat 640 g cod fillets dry with paper towels (dry surface = better glaze adhesion and browning). Season lightly with salt and pepper. Place the fillets on the empty half of the baking sheet (or use a separate sheet if your sprouts need more room), leaving a little space between pieces so air circulates. Spoon or brush a thin layer of the miso-citrus glaze over each fillet — a thin coat is better than a thick one so it heats through and caramelizes instead of burning.

Roast the fish: Slide the baking sheet back into the oven with the sprouts and roast everything together for 10–12 minutes (depending on fillet thickness). The hot oven cooks the fish quickly and the glaze will set into a glossy finish. Fish is done when opaque and flakes easily with a fork; internal temperature should be about 60°C (140°F) for moist, tender cod.

Finish the sprouts: In the last minute out of the oven, toss the roasted sprouts with toasted sesame seeds and, if using, a smashed garlic clove quickly sautéd in the remaining olive oil (or scrape the garlic oil onto the sprouts). The sesame seeds add texture and toasty flavor; the garlic oil gives a savory lift — add it at the end to keep garlic from burning.

Make the sweet potato & orange mash: Drain the cooked sweet potatoes and return them to the hot pot over low heat for 30 seconds to evaporate excess moisture — this concentrates flavor. Mash with a potato masher or ricer. Add the remaining olive oil (about 5–10 ml depending on how much you used for sprouts), 10 g butter (optional, for silkiness), 20 ml fresh orange juice and a pinch of salt and pepper. Stir in remaining orange zest to brighten the mash. Don’t overwork the potatoes — gentle mashing keeps the mash light rather than gluey.

Plate and garnish: Spoon a bed of the orange sweet potato mash onto each plate. Place a glazed cod fillet on top or alongside. Add a generous portion of the sesame-roasted Brussels sprouts. Finish with 1 tbsp chopped chives or cilantro per person (scatter half at plating and the rest at the table), and a tiny drizzle of the leftover miso glaze if you reserved some. Serve immediately so the glaze is glossy and the textures contrast.