Melt butter in a small saucepan over medium heat.

Add flour, stirring constantly to form a roux.

Cook the flour and butter for approximately 1 minute, stirring continuously.

Stir in milk and whisk constantly to prevent lumps.

As the mixture starts to thicken, reduce heat and continue to whisk until smooth.

Remove from heat when the sauce starts to boil.

Add 1 cup of cheese, dill, stock powder, salt, and pepper, stirring until the cheese is melted and the mixture is well combined.

Add cooked lobster meat (crayfish) and stir well to coat it in the sauce.

Spoon the lobster mixture back into the lobster shells, filling them generously along the entire length.

Sprinkle the remaining cheese over the filled shells.

Place the shells in a preheated oven at 200 degrees Celsius (392 degrees Fahrenheit) for 15 minutes, or until the cheese is browned and bubbly.

Remove from oven and let cool slightly before serving.