Persillade is a mixture of minced parsley and garlic. Used in French cooking, it is often employed to form a crust on meat.
Occasionally, some chefs will also add fresh white breadcrumbs.
You press the persillade into the surfaces of the meat (which are often coated first with Dijon, so that the Persillade will adhere better) before roasting.
Comes from the French name for parsley, which is “persil”.