In another frying pan over medium-high heat, add: 1/2 of the olive oil, and the rosemary. When sizzling, add the potatoes, cut side down. Roast for 9 min until golden. Meanwhile, in another frying pan over medium-high heat: the butter (swirl until the butter melts entirely), the shallots, and the green peppercorns. Cook for 2 min until the pan is almost dry.