Preheat oven to 400°F. Grease a 9" square pan or casserole dish.
Keeping the peel intact, gently scrub potatoes and remove any blemishes. Slice potatoes into 1/8" medallions.
In the pan, arrange the potatoes into rows by vertically lining up the medallions, being sure to alternate colors so a striped pattern forms. The potatoes should be packed tightly enough so they stand freely when the pan is full, but still have slivers of space between the tops.
When the pan is full, brush the olive oil over the rows of potatoes. Sprinkle with course sea salt and freshly ground pepper.
Bake for 25-30 minutes, or until the potatoes start to crisp on the top and the flesh is soft.