1. Peel the onion and carrots.
2. Wash the leek.
3. Finely slice the onion, celery, and leek.
4. Cut the carrots into small pieces.
5. Brown the chicken in butter and olive oil on both sides.
6. Reserve the chicken on a plate.
7. Pour the vegetables into a Dutch oven, scrape the bottom a bit to release the juices, and let cook for 10 minutes, stirring regularly.
8. Add flour, mix.
9. Return the chicken thighs to the Dutch oven, pour in the chicken broth and thyme sprigs.
10. Bring to a boil, then reduce the heat.
11. Cover and let simmer for 30 minutes.
12. When the chicken is cooked, remove it from the Dutch oven, remove the skin, and shred the meat with forks.
13. Place it back in the Dutch oven.
14. Add frozen peas, and let simmer uncovered for another 4 minutes.
15. Add vermicelli, and continue cooking for an additional 4 minutes.
16. Pour in the heavy cream, lemon juice, and pepper to taste.
17. Let it heat up, and serve immediately!
18. Tip: You can prepare this soup in advance, but without the vermicelli.
19. Add the vermicelli when reheating your soup (about 4 minutes of cooking in the simmering soup).