Put the potatoes in a large saucepan or pot of salted water and bring to a boil. The potatoes should not crowd the pan. Reduce the heat and simmer briskly for about 15 minutes or until tender when pierced with a fork. Drain the potatoes and return them to the pot.

With a fork or potato masher, smash the potatoes until almost smooth with a few lumps remaining. Drizzle with the olive oil and stir in the pesto. Season to taste with salt and pepper and serve hot.