Comforting soup flavoured with a smokey, salty ham hock, with celery root and carrots to brighten up the flavours.
In a large bowl, soak peas overnight with enough cold water to cover by 2 inches, and drain.
In a 7 quart heavy pot heat olive oil over medium heat, and add leeks. Cover and sweat leeks for 5 minutes until translucent. Avoid browning, they should still be white.
Tie the thyme and rosemary sprigs together with kitchen twine.
Add the sprigs to the pot, together with water, stock, ham hock, bay leaves and salt. Simmer, uncovered, for 45 minutes, skimming the foam from the top of the pot as it cooks. Once the peas are tender, remove the ham hock and reserve on a plate. Discard herb bundle and bay leaves. Using an immersion blender, puree the peas until smooth.
Peel the celery root and cut into 1/4" dice. Add to pureed soup and simmer, stirring occasionally for 20 minutes. Peel and dice carrots into 1/4" dice, add to pot and simmer until tender, about 15 minutes.
Remove meat from ham hock and discard skin and bones. Chop meat and add to soup. Give it a final taste check for salt and pepper. Serve sprinkled with fresh parsley and some freshly ground pepper.