Remove the skin and any fat from the chicken breasts and place them in a large saucepan. Add 800 ml of water, the bay leaf and the peppercorns. Bring to the boil and skim off any foam that comes to the top, then cover the pan and let the chicken simmer for 20 minutes, or until the meat comes off the bones easily. Leave it to cool for 5 minutes.
Lift the chicken from the liquid and slice the meat, or shred it with two forks, and set it aside. Strain the liquid and measure 150 ml into a bowl or jug. Add half the sweetcorn and purée it in a food processor or with a hand-held mixer. Return the purée to the pan, whisk in the remaining liquid and bring it to the boil.
Add the onions/leeks to the pan, then cover and simmer for 6-8 minutes until they are tender.
Add the cooked chicken to the chowder with the remaining sweetcorn and simmer for 2-3 minutes to heat both through. Taste and adjust the seasoning then serve hot, with crusty bread, if you like.
Variation: for a quicker version, substitute ready-cooked, skinned chicken breasts and use chicken stock instead of water, to enhance the flavour.