Whisk in lemon juice, Dijon mustard and olive oil until emulsified. Season to taste with salt and black pepper. Set aside at room temperature for flavors to meld.

Potato gratin

Preheat oven to 180°C (350°F). Lightly butter a medium baking dish.

Thinly slice potatoes (2–3 mm) using a knife or mandoline. Rinse slices briefly and pat dry to remove excess starch.

In a saucepan, combine cream, milk, minced garlic, thyme leaves, nutmeg, salt and pepper. Warm gently until just below a simmer, then remove from heat.

Arrange a layer of potato slices in the dish, overlap slightly. Pour some warmed cream mixture over the layer and sprinkle a little grated cheese. Repeat layering until all potatoes are used, finishing with cream and the remaining grated cheese on top.

Cover dish with foil and bake for 35 minutes. Remove foil and bake an additional 20–25 minutes until top is golden and potatoes are tender when pierced. Rest 10 minutes before serving.

Celeriac purée

Place diced celeriac and potato in a saucepan and cover with stock. Add a pinch of salt.

Bring to a simmer and cook until both are very tender (about 20–25 minutes). Drain, reserving a little cooking liquid.

Return vegetables to the saucepan. Add butter and use an immersion blender (or food processor) to purée until smooth, adding reserved cooking liquid or cream to reach a velvety consistency.

Stir in cream, taste and adjust seasoning with salt and white pepper. Keep warm.

Chargrilled asparagus

Preheat a grill pan or outdoor grill to high. Toss asparagus with olive oil, salt and black pepper.

Grill asparagus in a single layer, turning occasionally, until char marks appear and spears are tender-crisp, about 4–6 minutes. Keep warm.

Seabass and finishing

Pat sea bass fillets dry with paper towels. Season both sides with salt and pepper. Lightly dust skin side (and flesh side if you like) with flour and shake off excess.

Heat a large non-stick or stainless-steel skillet over medium-high heat until hot. Add olive oil and swirl to coat.

Place fillets skin-side down in the pan and press gently with a spatula for 20 seconds to prevent curling. Cook undisturbed for 3–4 minutes until skin is deep golden and crisp.

Flip fillets carefully and add butter to the pan. Baste the fish with melted butter for 1–2 minutes until just cooked through (internal temperature ~52–55°C / 125–131°F) but still moist. Remove from pan and keep warm.

Slice lemon in half and squeeze a little lemon juice over each fillet just before plating.

Plating

Divide potato gratin among 4 warm plates (about one generous slice or serving each).

Spoon a generous portion of celeriac purée beside the gratin.

Arrange 4–6 chargrilled asparagus spears next to the purée.

Place pan-fried sea bass fillet on top or beside the purée, skin-side up to keep crisp.

Spoon 1–2 tablespoons of salsa verde over the fish and a little around the plate for garnish. Serve immediately.