Scrub thin-skinned white or red potatoes (1 to 2 in. wide). Place them, no more than two layers deep, in a pan and cover them by about 1 inch of water. Set over high heat; just before water boils, reduce heat to maintain water temperature at 185° to 195° (when a few bubbles pop up from pan bottom regularly but surface of water is smooth). Cook, uncovered, just until potatoes are tender when pierced: for 1-inch diameter, about 25 minutes; 1 1/2 inches, 35 to 40 minutes; and 2 inches, about 50 minutes. Serve, or turn off heat and leave in water up to 30 minutes.