1-Step 1: Get everything ready (mise en place) Start by preheating your oven to 200°C (400°F; 180°C fan-forced). Pat the scallops dry and remove the side muscle if it is present, since that helps tenderness. Slice the scallops as needed based on size so each piece cooks evenly. Next, prep the cheesy crust by mixing the panko breadcrumbs, melted butter, shredded Gruyère, and a pinch of salt in a bowl. Set it aside. This way, when the sauce is ready, you can assemble quickly.

2-Step 2: Make the mushroom béchamel To begin the sauce, melt the butter over medium heat. Sauté the finely diced eschalot (or brown onion substitute) and diced white mushrooms until soft and aromatic, about 4 to 5 minutes. Sprinkle in the flour and cook for about 30 seconds, stirring until it looks pasty. Now stir in the hot milk and hot thickened cream. Keep whisking until smooth. Season with salt, black pepper, and nutmeg, then cook until the sauce bubbles for about 30 seconds, and remove from heat. You want it pourable, not thick like gravy.

3-Step 3: Season and assemble in shallow ramekins or scallop shells Season the scallops with salt, then divide them evenly into four shallow ramekins (about 11cm diameter and 2.5cm deep). Pour the béchamel over the scallops, filling gaps so the surface turns smooth when you level it. Top each portion generously with the breadcrumb-cheese mixture, making sure it covers fully. Using shallow dishes helps the sauce bubble and browns the crust evenly, which is the whole point of a gratinéed scallops dish.

4-Step 4: Bake, rest, and serve Bake on a tray for about 20 minutes until the top is golden and crisp. Rest for 2 minutes before serving so the sauce settles and the crust stays crunchy. For a polished look, serve hot with lemon wedges and a light garnish if you like.