In a pot heat up the oil, add the bay leaf, chopped onion and leek, stir and cook gently for about 4 minutes until softened, stirring often.
Push the mixture to the side, add the chicken pieces and cook for 2 minutes on each side.
Add the potatoes, carrot, celeriac and hot vegetable stock, cover and bring to the boil. Lower the heat and simmer for 30-35 minutes or until the vegetables are fully cooked. Stir occasionally.
Remove from the heat, carefully take the chicken out of the pot and place on a chopping board. Separate the meat from the bone, chop the meat roughly and put back into the pot along with the peas.
In a small bowl combine the corn flour with 2 tablespoons of hot water and stir until smooth. Heat up the soup again, add the flour mixture, stir and bring to the boil again. Simmer for 1 minute. Remove from the heat, season to taste and serve.
