Boil the potatoes for 10 mins or until tender. Drain and put back in the pan over a low heat for 30 secs to dry out. Mash with olive oil, orange juice, zest and seasoning, then spoon into a serving dish.
In a small saucepan, melt the butter with the sage leaves. Cook until it begins to foam and bubble, and small brown spots appear in the butter. Pour over the mash and serve.