Bring the fat to a simmer over medium heat in a wide saucepan; lower the heat and slip in the uncooked sausages to cook very slowly for 1 hour.
Pack sausages into clean dry jars with cooking fat to cover. Be sure they are well covered in fat. Cool completely before closing. Store in refrigerator until ready to use. Keep at least 1 week before using. Keeps 1 to 2 m