Peel the potatoes and cut into even size chunks.Put into a saucepan and cover with boiling water. Add a good pinch of salt then cover and simmer gently for about twenty five minutes.
Drain then return to the pan and cover with a damp teacloth for about five minutes to absorb some of the steam.
Mash the potatoes with a potato masher then add the pesto and salt and pepper, beating in with a wooden spoon or electric hand whisk. Reheat on a low heat if necessary.