Cut potatoes into 3-4cm pieces and place in heavy large pot. Cover with cold water. Boil over medium-high heat until potatoes are tender when pierced with fork, about 8-9 minutes.
Drain, reserving 11/2 cups of potato cooking liquid. Return potatoes to dry pot. Stir over medium heat until any excess liquid evaporates.
Add 6 tablespoons olive oil and mash until almost smooth. Mix in enough potato cooking liquid as needed to moisten.
Season to taste with salt and pepper. (Can be made 2 hours ahead. Let stand at room temperature. Rewarm over medium heat, adding more reserved cooking water as needed to moisten.)
Transfer potatoes to large bowl. Drizzle with remaining tablespoon olive oil and serve. Garnish with fresh herbs.
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