Lasagne alla ferrarese gets its green pasta by mixing spinach into the dough.
The dish comes from Ferrara, a historic city in Emilia-Romagna whose cuisine is known for elaborate fresh-pasta preparations. Spinach colors the dough naturally, producing green sheets that contrast with the sauces, cheeses, and other fillings used in the finished dish.
This is different from adding green herbs such as parsley or basil for flavor. The spinach is incorporated into the pasta dough itself, usually after being cooked, drained, and finely processed so it can blend with flour and eggs. The result is a tender fresh pasta with a distinctive color and a mild vegetal note.
Lasagne alla ferrarese may include pancetta, chicken livers, and other meats, so it should not be confused with the Bolognese version. Lasagne alla bolognese is commonly associated with green egg-pasta sheets too, but the question’s named Ferrara preparation specifically identifies spinach as the coloring ingredient.