1. Peel potatoes and place in a 3-quart pot, cover with cold water by 2 inches and bring to a boil over moderately high heat; add salt. Simmer until potatoes are fork tender but not falling apart, 20 to 25 minutes. Drain in a colander and when just cool enough to handle, cut into 1/2-inch cubes.
2. Preheat oven to 350 degree F and arrange rack in center. Heat oil in a 10-inch nonstick ovenproof skillet (if the handle is not ovenproof, wrap it tightly in aluminum foil) over moderate heat until hot but not smoking. Add potatoes and cook, stirring occasionally, until heated through, about 2 minutes. Whisk together flour, chives, baking powder, and pepper in a bowl. Whisk together eggs and cheeses in another bowl until combined well; whisk in flour mixture.
3. Pour egg mixture over potatoes and bake until firm and puffy, about 45 minutes. Let cool 5 minutes. Run a small knife around edge of frittata and gently slide onto a platter. Serve warm. Makes 8 servings.