Preheat oven to 180°C (350°F). Thinly slice potatoes (2–3 mm) using a mandoline or sharp knife. Rub a 20x20 cm (or similar) ovenproof dish with the halved garlic clove and the 1 tablespoon butter. Layer sliced potatoes in the dish overlapping slightly.

Make cream and bake

Combine heavy cream, milk, thyme, salt and pepper in a saucepan and warm until just below simmering. Pour warm cream over the potatoes so they are mostly submerged. Sprinkle grated Gruyère/Parmesan over the top. Cover with foil and bake for 35 minutes, remove foil and bake another 20–25 minutes until tender and golden on top. Allow to rest 10 minutes before serving so gratin sets.

Celeriac purée

Cook

Place cubed celeriac and optional potato into a pot and cover with stock. Add a pinch of salt. Bring to a simmer and cook until very tender, about 15–20 minutes.

Purée

Drain, reserving about 50 ml cooking liquid. Transfer vegetables to a blender or use an immersion blender. Add butter, cream and a little reserved liquid as needed and blend until silky. Season with salt, white or black pepper and a splash of lemon juice to taste. Keep warm.

Salsa verde

In a small bowl combine chopped parsley, capers, cornichons, chopped anchovy (if using), minced garlic, lemon juice and olive oil. Season with salt and pepper, stir well and taste — adjust acidity or seasoning. Leave at room temperature for flavors to marry while you cook the fish and vegetables.

Chargrilled asparagus

Preheat a grill pan or ridged skillet over medium-high heat until smoking slightly. Toss trimmed asparagus with 1 tablespoon olive oil, salt and pepper. Place asparagus in a single layer on the hot pan and cook, turning occasionally, until char marks appear and stalks are tender-crisp, about 6–8 minutes. Keep warm.

Seabass & plating

Season and dust

Pat sea bass fillets dry with paper towel. Season both sides with salt and pepper. Lightly dust the skin side (and skin edge) with the 3 tablespoons flour, shaking off excess.

Pan fry

Heat a large nonstick or stainless steel skillet over medium-high heat. Add 2 tablespoons olive oil until shimmering. Place fillets skin-side down and press gently with a spatula for the first 20 seconds to keep skin flat. Cook skin-side down for 3.5–4 minutes without moving, until skin is crisp and the fish is cooked about two-thirds of the way through. Flip carefully, add 1 tablespoon butter and baste for 30–60 seconds until fish is just cooked through (internal temp ~52–55°C/125–130°F). Remove to a warm plate and rest briefly.

To plate: Spoon a generous smear of celeriac purée onto the center of each plate. Cut a square or scoop of potato gratin and place slightly overlapping the purée. Arrange chargrilled asparagus alongside. Place the seabass fillet on top, skin-side up angled attractively. Spoon 1–2 tablespoons of salsa verde over the fish and a little around the plate. Garnish with microgreens or parsley and serve with lemon wedges.