Rinse the lentils under cool running water and add to a medium saucepan. Cut the celery into pieces a few inches long and add to the saucepan along with the peeled garlic cloves. Add enough water to cover by a few inches, then bring to a simmer and cook until very tender, 30 - 40 minutes.
Meanwhile, bring another medium saucepan of water to a boil. Add the sausages and boil until cooked through, about 10 - 15 minutes.
When the lentils are tender, discard the celery and garlic then plate them using a slotted spoon, then top with slices of cooked sausage. Drizzle with olive oil and sprinkle with salt to finish.
Recipe by The Taste Edit at https://thetasteedit.com/umbrian-castelluccio-lentils-and-sausage/