Years ago, I picked up a copy of ..."L´arte de mangiar bene" by Pellegrino Artusi, originally written in 1894.
He´s got a recipe for conchiglie ripieni ( stuffed shells):
130 gms fish fillet
20 gms Parmesan
Bechamel (20 gms flour, 20 gms butter, 2.5 decilitres milk)
2 egg yolks
Poach the fish and allow to cool.
Make the bechamel, then add the parmesan and egg yolks when it has cooled. Mix well then add the fish, folding it in gently. Salt and pepper.
Stuff the shells and cover with extra bechamel, put under the grill until just browned.
Then when I looked closer at the recipe, I discovered the recipe was actually not conchiglione, but large clam shells
Obviously I need to brush up on my Italian...
One recipe I found for conchiglioni was stuffed with spinach, ricotta and mozzarella - with an added egg - covered with tomato sauce, then baked. was stuffed with ricotta, artichokes and rocket leaves.
About a dozen recipes for conchiglie, mind you, which could easily be adapted.