What seed is the signature filling of St. Martin's croissant?

The signature filling of St. Martin’s croissant is white poppy seed.

Known in Polish as rogal świętomarciński, this regional pastry uses a rich filling based on white poppy seeds, usually combined with sugar, crumbs, eggs, nuts, raisins, and candied or preserved fruit. Almond flavoring and a sugar glaze are also characteristic of many versions.

White poppy seeds are milder and less assertive than the dark poppy seeds commonly associated with Central European pastries. That distinction matters because “poppy seed filling” alone can conceal the specific ingredient that defines the protected Poznań specialty.

The filling is enclosed in semi-laminated yeast dough, which is shaped into a crescent and finished with icing and chopped nuts. Caraway, sunflower, and sesame seeds may appear in other breads or pastries, but they are not the signature filling ingredient of St. Martin’s croissant.