Rinse the Whole Chicken and remove any giblets; place the chicken in a large stockpot and cover with Water (about 8–12 cups, enough to submerge the bird). Bring to a gentle boil over medium-high heat, skimming off any foam that rises to the surface.
Trim, halve lengthwise, and wash the white and light-green parts of the Leek; add them to the pot along with the Bay Leaf, a teaspoon of Black Peppercorns, a few sprigs of Thyme, and a pinch of Fine Sea Salt. Reduce heat to low and simmer gently, covered, for 1 to 1½ hours until the chicken is very tender.
Carefully remove the chicken from the pot and set aside to cool slightly. Strain the broth through a fine sieve into a clean pot, discarding the solids (reserve the leeks if you like some soft pieces in the finished soup).
When the chicken is cool enough to handle, shred the meat from the bones and discard skin and bones. Return the strained broth to a simmer and add the White Rice and the Prunes; simmer until the rice is tender and the prunes have plumped, about 15–20 minutes.
Taste the soup and adjust seasoning with more Fine Sea Salt if needed and freshly ground Black Pepper to your liking. Stir the shredded chicken back into the pot to warm through for a few minutes.
Finish by stirring in chopped Parsley for a fresh, herbal lift. Serve the Cock-a-Leekie hot with crusty bread or oatcakes.
