Use a medium-starch potato, such as Yukon Gold for the best results. These potatoes will hold their shape after boiling, but are starchy enough to develop some rough edges for crisping during the roasting period. Avoid waxy potatoes, such as red, as they won't develop soft creamy centers when roasted, and also won't have crispy edges. Don't use high-starch potatoes, such as Russets, as they won't hold their shape after boiling.