Spring Scallion and Jumbo Lump Crab Mornay Gratin

Preheat the oven to 190°C (375°F) with a rack positioned in the center.

Spread the crab meat over paper towels set on a rimmed baking sheet, inspect gently by hand to remove any lingering bits of shell, and pat the top dry.

Melt 30g of unsalted butter in a medium saucepan over medium-low heat (approximately 120°C / 250°F surface temperature), then add the sliced scallion whites and minced garlic.

Add the all-purpose flour to the saucepan and whisk constantly to form a smooth blonde roux.

Pour in the whole milk and heavy cream in a steady stream while whisking continuously to prevent lumps, then bring the mixture to a gentle simmer at 85°C (185°F).

Reduce heat to low (around 65°C / 150°F), add the softened cream cheese and shredded Gruyere cheese, and stir until completely melted and glossy.

Whisk in the Dijon mustard, fresh lemon juice, Old Bay seasoning, fine sea salt, and black pepper until fully combined.

Remove the saucepan from the heat, add the picked crab meat and half of the sliced scallion greens, and fold very gently with a silicone spatula.

Transfer the crab mixture into the 1.5-liter ceramic gratin dish and spread into an even layer.

Combine the panko breadcrumbs and remaining 15g melted butter in a small mixing bowl, tossing until evenly moistened, then scatter over the gratin surface.

Bake in the preheated oven at 190°C (375°F) until the sauce is actively bubbling around the edges and an instant-read thermometer inserted into the center reads at least 63°C (145°F).

Switch the oven setting to broil on high at 260°C (500°F) and broil for 1 to 2 minutes, watching closely until the crumb topping turns deep golden brown.

Remove the gratin from the oven, let rest on a heatproof surface for 5 minutes, then scatter the remaining sliced scallion greens over top and serve hot.