Put the soaked peas into a saucepan. Add the onion, carrot and bay leaves and cover with the stock. Bring to the boil, skimming off any scum from the surface if you need to.
Lower the heat and simmer for about an hour or until the peas have softened and most of the liquid has been absorbed.
Remove the bay leaves and tip the veg and peas into a blender. Blitz to a puree, then pour into a clean saucepan. Add the vinegar and butter, reheat gently then season with salt and pepper before serving.