Start with the beef jus. Pour the stock into a small saucepan and bring to a simmer over medium heat. Let it reduce slowly until thick, glossy and intensely flavoured — you want it to coat the back of a spoon. This should take around 30–40 minutes. Skim off any foam that rises to the top, and set aside to reheat just before serving.

While the jus reduces, prepare the potato scales. Peel the potatoes and slice them into paper-thin rounds using a mandolin. Use a small ring cutter (about 2.5cm) to punch out uniform discs. Blanch the discs in boiling salted water for 1 minute to soften them slightly, then drain. While still warm, toss gently with a tablespoon of melted butter so they don’t stick together.

Pat the red mullet fillets dry and lay them skin-side up on a tray or board. Brush them with butter. Starting from the tail end, layer the potato discs across the skin, overlapping slightly like fish scales until the whole surface is covered.

For the orange butter sauce, pour the strained orange juice into a small saucepan and reduce gently over low heat until slightly thickened and more concentrated — about 5–7 minutes. Remove from the heat and whisk in the cold diced butter, a few pieces at a time, until emulsified and glossy. Stir in the crème fraîche and season with a pinch of salt and a few drops of white wine vinegar if it needs a little sharpness.

To cook the fish, heat a large non-stick frying pan over medium heat and add a knob of butter. Place a sheet of baking paper in the pan and lay the fillets potato-side down on top of it. Gently press down or place a second pan on top as a weight. Cook for 3–4 minutes without moving them — the potato should turn golden and crisp while the fish cooks through gently. Baste the flesh side with hot butter from the pan to keep it moist.

When the potato scales are crisp and the fish is just cooked, gently lift out the fillets and remove the baking paper.

To serve, place two fillets on each plate, spoon over the orange butter sauce and finish with a drizzle of the beef jus around the edge. Serve immediately.