In large stockpot over medium-high heat, combine chicken stock, beef stock, white wine, water, bay leaf, thyme, parsley and garlic.
Season chicken legs with salt and pepper; add to pot. Add potatoes, Brussels sprouts, celery and parsnips.
Bring to a boil over high heat, cover and decrease heat to a gentle simmer. Cook until vegetables are almost tender, about 15 minutes.
Use tongs to gently move ingredients around. Continue to simmer, partially covered, until chicken is almost cooked through, about 15 minutes more.
Add green beans and leeks and continue cooking until chicken is completely cooked and vegetables are tender, about 7 minutes.
Dice chicken and vegetables on plate. Ladle over broth in soup bowls.
Serve hot, accompanied by mustard, pickles and horseradish.8 To serve, ladle broth into soup bowls. Serve with slices of baguette.