For the snail butter, chop the garlic, shallot and parsley as finely as possible. Knead under the softened butter with a fork, season with salt and pepper. Brush off the mushrooms and twist out the stems.
Heat water in a saucepan, add the lemon juice and season with salt. Cook the mushrooms in it for 5 minutes, remove and drain. Finely chop the shallot and the mushroom stalks and bake in a pan for 5 minutes while stirring. Preheat the oven to 180 degrees.
Butter an oven pan or 6 individual molds, place the mushrooms in them and fill with the shallot-mushroom mixture. Put a snail on top then a nut snail butter. Bake in the oven for 10 minutes and serve hot with a baguette.