Heat oven to 425 degrees.
Halve potatoes and toss in a large bowl with olive oil, salt and pepper. Pluck a piece of rosemary or thyme smaller than the width of the potato and press onto the cut side. Place cut-side down on a large, light-colored, heavy-bottomed baking pan about 1 inch apart.
Roast at 425 degrees for 35 minutes, or until potatoes are fork-tender and cut side is browned.