Rather than just spreading a baguette with a flavorful topping, here the topping becomes a filling that's used to stuff a hollowed out baguette, so that there's a wonderful surprise center in every slice. The filling is a savory spread of mayonnaise, dried sea vegetables, boiled egg, onion, and parsley. The filed baguette will need to be chilled a bit to allow the mayonnaise mixture to firm up enough to slice, and you can even do this a day ahead.