1) In a large saucepan, add the potatoes and water to cover by 2 1/2cm. Bring to the boil over high heat.
2) Lower the heat to a simmer and cook the potatoes until tender, about 25 to 30 minutes. Dry by setting out on a board or in a colander.
3) Quarter the potatoes and set on a baking sheet in one layer to dry. Once they're dry, place the potatoes in a bowl. Mash with a fork until broken up but not smooth.
4) Add the pepper, chives, thyme and tarragon. Season with salt. Mix well. Add the oil 120ml at a time. You may find you do not need all of the oil. Add the lemon zest, if using. Mix well.
Chef's note: Cook the potatoes whole so they don't get waterlogged, which dilutes the flavour.