Pan‑roasted sea bass with lemon‑butter sauce, crushed rosemary potatoes and wilted spinach
A romantic, restaurant‑style fish supper for two: crisp skin sea bass, glossy lemon‑butter sauce and crunchy crushed potatoes.
This is the sort of dish that looks far more complicated than it is — perfect for a date night when you want to impress but not be stuck in the kitchen. Crisp skin, glossy lemon‑butter and crunchy smashed potatoes give contrast that feels thoroughly grown‑up.
It comes together in about 45 minutes and scales easily. The crucial moments are drying the fish for a crisp skin and resting it briefly so the flesh stays juicy — get those right and you’ll be very popular.
Ingredients
- 2 sea bass fillets — about 160–200g each, skin on
- 500 g new potatoes
- 2 sprig fresh rosemary
- 60 g unsalted butter — use all during the recipe (potatoes, basting, sauce)
- 30 ml olive oil — total for frying and cooking
- 1 lemon — zest and juice from half, wedges to serve
- 1 brown shallot — finely sliced
- 2 garlic — crushed or finely chopped
- 150 g baby spinach
- 75 ml dry white wine
- 150 ml fish stock — made from concentrate or a cube to this volume
- sea salt — to taste
- freshly ground black pepper — to taste
- 10 g flatleaf parsley — finely chopped for garnish
Equipment
- colander
- tongs
- fish spatula or turner
- microplane or zester
Instructions
Scrub the new potatoes and halve any larger ones so pieces are roughly equal. Put them in a saucepan, cover with cold water, add a pinch of sea salt and bring to the boil. Simmer until tender when pierced with a knife, about 16 minutes.
While the potatoes cook, finely slice the brown shallot and crush the garlic. Zest the lemon and cut it in half. Pat the sea bass fillets dry with kitchen paper, then season both sides with sea salt and freshly ground black pepper.
Drain the potatoes and return them to the saucepan. Lightly smash each piece with a fork (do not puree). Stir in 20g of the unsalted butter and one fresh rosemary sprig, season to taste and set aside while you crisp them.
Heat a frying pan over a medium heat with about 10ml olive oil. Add the smashed potatoes in a single layer (do in two batches if needed) and fry until golden and crisp, turning once, about 7 minutes.
Wipe the pan clean and return to a medium‑high heat with 10ml olive oil. Place the sea bass fillets skin‑side down and press gently with a fish spatula or turn‑out spatula for 20 seconds so the skin makes full contact. Cook skin‑side down, undisturbed, until the skin is deeply golden and crisp, about 6–7 minutes.
Flip the fillets, add 20g unsalted butter to the pan and baste the fish with the melting butter for 60–90 seconds; finish with a squeeze of lemon juice. The flesh should feel just firm and opaque.
Transfer the sea bass to a warm plate and rest for 10 minutes while you finish the sauce and greens.
In the same pan, add a little of the remaining olive oil if needed and gently fry the brown shallot and garlic over a medium heat until softened, about 3 minutes.
Pour in the dry white wine and let it reduce by about half, roughly 3 minutes, then add the fish stock and simmer until the liquid has reduced by about a third, roughly 5 minutes.
Remove the pan from the heat and whisk in the remaining 20g unsalted butter until the sauce is glossy. Stir in the lemon zest, a squeeze of lemon juice to taste and most of the chopped flatleaf parsley (reserve a little for garnish). Season with sea salt and freshly ground black pepper.
Meanwhile, wilt the baby spinach in a clean frying pan with a splash of olive oil and a pinch of sea salt over a high heat — it takes about 1–2 minutes. Drain any excess liquid.
To serve, spoon some sauce onto warm plates, pile the crushed rosemary potatoes, top with a sea bass fillet and spoon more sauce over. Add a little wilted spinach and scatter the reserved flatleaf parsley and lemon wedges.
Tips
- Pat sea bass completely dry and season just before cooking — damp skin prevents proper crisping.
- Smash the potatoes with a fork, not a masher, so they keep rough edges that crisp up in the pan.
- When making the sauce, add the final butter off the heat and whisk — this keeps the sauce glossy and stable.
- You can cook the potatoes ahead and re‑crisp them in the pan just before serving to save time.
- If you don’t have fish stock, use light vegetable stock — the sauce will be fine but slightly less briny.
Substitutions
sea bass fillets → sea bream fillets, same weight
Stays closenew potatoes → baby potatoes, same total weight
Stays closeunsalted butter → olive oil or dairy‑free spread (use same weight), for a dairy‑free version
Noticeably differentdry white wine → extra 75ml fish stock with 1 tsp white wine vinegar
Stays close
Nutrition
Per serving · estimated
- 850
- Calories
- 45 g
- Protein
- 45 g
- Carbs
- 52 g
- Fat
- 4 g
- Fibre
- 3 g
- Sugar
- 650 mg
- Sodium
FAQ
Can I use frozen sea bass?
Yes — fully defrost in the fridge, pat very dry and cook as instructed. Frozen fish often holds more water, so drying is even more important.
How do I know when the fish is cooked?
Cook until the flesh is opaque and flakes with a fork. For fillets 160–200g, total pan time is typically 7–9 minutes depending on thickness.
Can I make the potatoes ahead?
Yes — boil and smash the potatoes up to a day ahead, chill, then reheat and crisp in the pan for 6–8 minutes before serving.
How do I keep the sauce from splitting?
Whisk in cold butter off the heat and keep the sauce at a gentle warmth rather than a rolling boil; this helps it emulsify rather than separate.
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