Preheat oven to 400 degrees F. Line a baking sheet with foil.
Wash potatoes. If you have a variety of sizes, slice the large ones in half, but leave smallest ones intact. Transfer them to the baking sheet. Drizzle with olive oil, rosemary, lemon zest, and sea salt. Mix until evenly coated. Top with slices from the same lemon, and a few extra sprigs of rosemary.
Bake for 25 to 30 minutes or until potatoes are golden brown and tender. Serve with more rosemary, to taste.