Peel the onion and garlic.
Check the pheasant for any remaining feathers and remove them, then place the bird in a large pot.
Add enough water to fully cover the pheasant. Add the onion and garlic and bring to a gentle boil.
As the water heats, foam will rise to the surface. Skim this off with a mesh spoon.
Add the stock cubes and a bay leaf. Cover the pot and simmer gently for 75 minutes.
Meanwhile, peel the root vegetables (celeriac, swede, carrots, parsnip, potato) and cut them in half.
Add the vegetables to the pot, bring it back to just below boiling point, and simmer for another 1 hour.
Add the peas and kale and cook for 15 minutes more.
While the soup finishes cooking, prepare the small pasta according to the packet instructions.
Remove the pheasant from the pot and transfer it to a plate. Strip the meat from the carcass, discarding the bones, and shred the meat into bite-sized pieces.
To serve, place a large spoonful of cooked pasta into each bowl, add some shredded pheasant and vegetables, then ladle over the hot broth.
Finish with a sprinkle of chopped parsley and serve immediately.