Which soup is known for including leeks and chicken?

The soup known for including leeks and chicken is Cock a Leekie. This traditional Scottish dish typically consists of a rich broth made from chicken and leeks, often enriched with other ingredients such as carrots, barley, and even prunes for added flavor. The name itself is a nod to its primary ingredients, with "leek" being a prominent component that contributes to the soup's distinct taste and aroma.

In contrast, Tom yum is a Thai soup featuring flavors such as lemongrass, lime, and chili, and is primarily seafood-based. Chef's soup can vary widely but is not specifically defined by leeks or chicken. Clam chowder, especially associated with New England cuisine, prominently features clams, potatoes, and cream but does not use leeks or chicken as key ingredients. Therefore, Cock a Leekie stands out as the correct answer.