Boil the potatoes whole in salted water for 10–12 minutes until just tender. Drain and let cool slightly.
Halve or squash gently with the back of a spoon to expose more surface.
Heat the olive oil and butter in a large frying pan over medium-high heat.
Add potatoes and cook cut-side down until golden and crisp (~4–6 minutes). Flip and crisp the other sides.