Preheat oven to 425o F with rack in lowest position

Generously cover potatoes with cold water in a 4-quart pot and add 1 T salt. Bring to a boil, then simmer, partially covered, until potatoes are just tender when pierced with a small sharp knife, about 12 minutes. Drain. Cool potatoes to warm, then peel and cut in half crosswise.

Cook bacon in a 12-inch heavy skillet over medium heat, stirring until cooked through but still flexible. Drain on paper towels, reserving fat in skillet.

Brush bottom of a 15- by 10-inch shallow baking pan with oil and half of the reserved bacon fat. Sprinkle potatoes with ½ teaspoon salt and ¼ teaspoon pepper and arrange, cut sides down, in baking pan. Bake until undersides are brown, 30 to 35 minutes.

Reduce oven temperature to 375oF. Turn potatoes over, then sprinkle with cheese, bacon, and garlic and drizzle with remaining bacon fat (if fat congeals, reheat briefly over medium heat).

Bake until cheese is melted, about 15 minutes.