Preheat broiler to high. Gently pick over crab meat for shells. Lightly grease 4 crab shells or ramekins.

In a saucepan over medium heat, melt butter. Add shallots and cook until soft, about 3-4 minutes.

Sprinkle flour over shallots, cook and stir for 1 minute to make a roux. Whisk in the sherry until a smooth paste forms.

Gradually whisk in the heavy cream. Cook, whisking, until the sauce thickens and coats a spoon, about 4-5 minutes. Reduce heat to low.

In a separate bowl, whisk egg yolks. Slowly ladle about 1/2 cup of hot sauce into the yolks while whisking constantly to temper. Pour the tempered yolk mixture back into the saucepan.

Remove from heat. Stir in Dijon mustard, salt, peppers, and 1/2 cup of the Gruyère cheese until melted.

Gently fold in the crab meat and parsley. Divide the mixture among the prepared shells or ramekins.

In a small bowl, combine the remaining 1/2 cup Gruyère and the Panko breadcrumbs. Sprinkle over the crab mixture.

Place on a baking sheet and broil for 2-4 minutes, watching closely, until the topping is golden brown and bubbly. Serve immediately.