What medieval cookbook contains the first recorded lasagna recipe?

The medieval cookbook containing the first recorded lasagna recipe is the Liber de Coquina.

The Liber de Coquina, or “Book of Cookery,” is an anonymous medieval cookbook associated with the Naples area. Its surviving manuscripts date from the early 14th century, although the material itself was compiled around the transition from the 13th to the 14th century. The work includes a recipe for lasanis, made from sheets of dough that are boiled and dressed with cheese and spices.

This recipe differs substantially from the lasagna commonly served today. It does not use tomatoes, since tomatoes arrived in Europe from the Americas only after the late-15th-century voyages of Christopher Columbus. Nor does it necessarily describe the modern layered casserole of meat sauce, béchamel, and cheese. It is better understood as an early documented form of pasta sheets prepared with seasonings.

The Forme of Cury contains a somewhat similar English dish called loseyn, but it is not the cookbook credited with the first recorded lasagna recipe. De re coquinaria is much older Roman cookery, not a medieval lasagna source.