Est. 1941. Gumbo File, dried and ground sassafras leaves, thickens as well as flavors food. Add to traditional cajun dishes like gumbo, jambalaya, or creole sauce. Do not boil after adding Gumbo File or it will turn stringy. www.spiceislands.com. Gumbo File, dried and ground sassafras leaves, thickens as well as flavors food. Add to traditional Cajun dishes like gumbo, jambalaya or Creole sauce. Do not boil after adding Gumbo File or it will turn stringy.