Step 1Break bay leaf into pieces and set aside. Peel and finely chop garlic. Cut ends off onion, then peel and chop onion into small pieces.
Step 2Put garlic, onion, milk, broth, vinegar, butter, bay leaf pieces, salt and pepper in medium saucepan. Place pan over medium-low heat and slowly bring to almost boiling, about 25 minutes; this allows flavors to develop.
Step 3While sauce is heating, tear bread into small pieces and set aside. Prepare spinach by rinsing and patting dry with paper towels. Chop leaves into pieces.
Step 4When sauce is about to boil, reduce heat to low and stir in bread pieces and chopped spinach. Add chicken pieces to sauce. Cover pan and simmer 20 minutes, making sure sauce never boils. Remove lid and turn chicken pieces over. Cover and cook 20 more minutes or until chicken is done. Immediately serve in deep dishes or bowls, using enough sauce to cover chicken pieces.