1. Cut the pork meat into pieces.
2. Peel and chop the shallots.
3. Peel the onion and stud it with cloves.
4. Clean and slice the leeks and celery stalk into pieces.
5. In a casserole dish, sauté the pork pieces, the onion studded with cloves, the chopped shallots, the flour, and the bouquet garni. Mix well and cover with water.
6. Cover the casserole dish and let it cook for 30 minutes over low heat.
7. Then add the leek and celery pieces, followed by the split peas. Stir well.
8. Let it cook for another 30 minutes over low heat and covered.
9. Finally, add the whole Morteau sausages and cook again for 25 to 30 minutes over low heat and covered.
10. After this time, remove the Morteau sausages from the casserole dish, slice them into rounds, and keep them warm.
11. Use an immersion blender to blend the split pea soup with vegetables to your desired consistency. Season with salt and pepper to taste.
12. Pour the split pea soup into bowls or deep plates.
13. Add the slices of Morteau sausages to each bowl.
14. Serve immediately with toasted bread croutons.