Charring salad onions brings out their natural sweetness, which works brilliantly with delicate white fish. Serve with salad onion-infused mash (inspired by Irish champ) drizzled with nutty, umami-rich brown butter.
- CourseMain meal
- Prepare15 mins
- Cook30 mins
- Total time45 mins
Put the potatoes in a large pan and add cold water to cover. Add a pinch of salt and bring to the boil, then simmer for 15-20 minutes until tender. Meanwhile, trim and thinly slice 1½ bunches of salad onions (setting aside the very dark-green trimmed ends). Put in a small pan with the milk and heat until just starting to bubble. Take off the heat, cover and set aside to infuse.
Meanwhile, in a bowl, mash 60g butter with the finely chopped dill and lemon zest; season. Preheat the grill to medium-high. Make 3 diagonal slashes on each side of the fish. Rub the fish on both sides with 1½ tbsp oil and season.
Put in a roasting tin, then stuff each fish cavity with ¼ of the butter mixture and the reserved dark-green trimmings. Drizzle the remaining whole salad onions with the remaining oil and add to the roasting tin. Cook under the grill for 10-12 minutes, turning both the fish and onions halfway through, until the fish skin is crispy and the flesh is opaque and cooked through.
While the fish is cooking, make the brown butter. In a small pan, melt the remaining 100g butter over a low-medium heat, then continue to bubble, swirling the pan every so often for 2-3 minutes, until the butter starts to turn brown and smell biscuity; take off the heat straight away and tip into a bowl.
When the potatoes are cooked, drain them, then return to the pan and cook over a low heat for 2 minutes, shaking the potatoes occasionally to dry them out. Take off the heat, pour in ½ the brown butter, then use a potato masher to mash until smooth. Reheat the milk and sliced salad onions until steaming hot, then gradually beat into the potatoes until creamy; season.
Scatter the cooked fish with the remaining dill fronds and serve on warm plates with the champ and the remaining brown butter drizzled over. Peel the charred skins from the salad onions (or just chop off the charred ends if they are slim ones) and serve alongside with the lemon wedges for squeezing.