The Sandwich Préfou is built on a garlic-butter bread, and the bread is the whole idea. Préfou is a Vendée flatbread: a soft, low, lightly baked white loaf split horizontally and loaded inside with butter mashed together with crushed garlic, then closed and warmed through so the butter melts into both faces of the crumb and the garlic perfumes the whole loaf. To make it a sandwich you treat the garlic-buttered bread as the structure and slip a thin filling into it, or you eat it as it is, the molten garlic interior doing the work a filling usually does. The region is Vendée.
The craft is the behavior of the garlic butter under heat. Préfou is not a crusty bread; it is soft and pale by design, baked only enough to set, so when it is warmed the interior butter liquefies and saturates the crumb rather than running out of it. That saturation is the point and also the constraint: the loaf is rich and already fully seasoned, so anything added has to be light and restrained or it buries the bread it was meant to ride in. A few slices of a mild cured ham, a little soft cheese, a leaf of something cool: these read as accents against the garlic butter rather than as the main event. Add too much, or anything assertive, and you have lost the préfou. Warmth is essential. Cold, the butter sets waxy and the garlic turns harsh; warm, it is soft, fragrant, and almost spreadable straight through the loaf. It is a sandwich best eaten within minutes of coming out of the oven, which is also how it is served, warm and torn or cut into lengths to share.
Variations are small and stay close to the bread, the garlic heavier or lighter, herbs worked into the butter, sometimes a thin layer of ham or cheese tucked in before it is warmed. The restraint is the constant. The Sandwich Préfou belongs with the regional preparations the catalog groups under Plat-en-Sandwich, the Vendée and broader local specialties that become a sandwich on their own terms. Its specific contribution is a soft garlic-butter loaf that is filling and bread at once, a sandwich whose discipline is to keep almost everything else out.