Wash the meat. Wash, clean, quarter and seed the tomatoes. Cut flesh into fine strips. Put the tomato inside in a pot with the chicken stock and puree in it. Add meat, bring to the boil and simmer covered for about 15 minutes.
Remove the chicken filet, let it cool down a little and cut it into strips. In the meantime, clean and wash the leek and cut it into fine strips. Wash the thyme, remove the leaves from the stems and chop.
Peel garlic and crush finely. Heat the fat in a pan. Sauté garlic and leek in it. Add to the soup with the tomato and chicken strips, heat and season with salt, pepper and thyme.