Preparation Cover potatoes with cold water by 1 inch in a 4- to 5-quart pot and add salt, then bring to a boil. Reduce heat and simmer, partially covered, until potatoes are tender when pierced with a sharp knife, 15 to 20 minutes. Meanwhile, cook milk and cheese in a 2-quart heavy saucepan over low heat, stirring occasionally with a whisk or wooden spoon, just until cheese is melted and sauce is smooth (do not boil), 8 to 10 minutes. Remove from heat and stir in speck. Drain potatoes in a colander and cut in half. Serve with sauce poured over them.