For the stock, heat grapeseed oil on a medium heat in a large stock pot. Add onion and fry gently until starting to soften, then add garlic and continue to fry until tender. Add the celery and carrots for a few minutes.
Add the rest of the ingredients with 4 litres of water and bring to a very gentle simmer, skimming the surface fat off regularly. Once the celery and carrot are tender, about 5-10 minutes, remove them from the pot and reserve.
Simmer stock very gently for about 3 hours over low heat, until the hock falls easily away from the bone. Shred the hock into large pieces of meat and reserve. Strain stock, season with salt and white pepper.
Put the strained stock back on the stove, bring it to a simmer, add the chicken breasts and turn to the lowest setting. Poach for 12 minutes. Remove pot from heat for a further 15 minutes. Remove chicken breasts from the stock and allow to cool, then shred.
You should have about 2 litres of stock remaining; add water to make up this amount, if needed. Add the kipfler potatoes, bring to a simmer and cook until tender, about 12-15 minutes.
Add silverbeet, ham hock meat and chicken to the pot with the reserved celery and carrots. Warm through, adjust seasoning to taste and serve in bowls, ensuring you get a good mix of all the ingredients in each bowl. Garnish with parsley and chervil and freshly ground black pepper.