Cut the bacon and onion into small cubes and fry in the oil until translucent. Halve the leek and cut into thin slices, dice the carrots and celeriac. Put everything in the fat and sweat.
Rinse the lentils and add them to the saucepan with the stock, the diced potatoes and the bay leaf. Let everything simmer for about 30 minutes. Season to taste with salt and pepper. Cut the sausages into slices and add.
If you like it sweet and sour, you can add a tablespoon of sugar and a tablespoon of vinegar at the end.