Question: One time I was at a French restaurant and they served, as an appetizer, snails over puff pastry with a sauce. Do you have any idea what I had?
Answer: Hi Brian. Thanks for writing in with your question. Sounds like a pretty tasty way to enjoy snails.
As far as I know there is no particular traditional dish that fits this description. However, it certainly is a popular way to fix escargot as well as seafood. You would also quite likely find it served in a larger portion as a main dish.
Typically, the sauce would just be a rich white cream sauce, something like this sauce suprême. Here in France, one can easily buy prefabricated mini puff pastry shells, making this a fairly easily replicated dish at home.
As for a name, Petits feuilletés aux escargots would probably most accurately describe this dish.