The Crêpe Sucrée Garnie is less a single sandwich than a format with the filling left open. A wheat-flour crêpe is cooked thin on the crepière, dressed with whatever sweet element the cart or crêperie is built around, and folded into a wedge or rolled into a cone for eating in the hand. The garnie part of the name is the operative word: it signals that this is the dressed-up end of the sweet-crêpe spectrum, the one with fruit, confiture, chestnut cream, chantilly, or some combination, as opposed to the austere sugar-and-butter baseline.
The crêpe itself is the constant, and its quality decides the sandwich more than the filling does. A good one is barely structural, lacy at the edges, pliable enough to fold around a wet filling without cracking, cooked just past the point where it stops tasting of raw flour. The technique that matters is heat timing: the filling goes on while the crêpe is still warm enough to loosen a confiture or melt a chocolate, but not so hot it liquefies cream or collapses the fold. The standard moves are banana with chocolate spread, apple compote with a dusting of cinnamon, chestnut cream with a curl of crème fraîche, or simply seasonal fruit with sugar and a squeeze of lemon.
This sits at the broad, improvisational end of a family whose more codified members each have their own article: the Crêpe au Sucre and Crêpe Beurre-Sucre at the minimalist extreme, the Crêpe Nutella-Banane as the single most-ordered combination. The wider Crêpe & Galette Salée tradition covers the savory Breton side of the same batter culture, where buckwheat galettes carry a complete meal rather than a dessert. The Sucrée Garnie's place in all of it is to be the open category, the one a crêpe stand uses to sell whatever is good and in season without having to name every permutation.