Step #1 Peel potatoes & place this in a 3-quart pot, cover with cold water by 2 inches & bring to a boil over moderately high heat; add salt.
Step #2 Simmer until potatoes are fork tender but not falling apart, 20-25 mins.
Step #3 Drain in a colander & when just cool enough to handle, cut into 1/2-inch cubes.
Step #4 Preheat oven to 350 degrees & arrange rack in center of oven.
Step #5 Heat oil in a 10-inch nonstick skillet (if the handle is not ovenproof, wrap it tightly in aluminum foil wrap) over moderate heat until hot but not smoking.
Step #6 Add potatoes & cook, stirring every once in awhile, until heated through, about 2 mins.
Step #7 Whisk together flour, chives, baking powder & pepper in a bowl.
Step #8 Whisk together eggs & cheeses in another bowl until well mixd; whisk in flour mixture.
Step #9 Pour egg mixture over potatoes & bake this until firm & puffy, about 45 mins.
Step #10 Let cool 5 mins.
Step #11 Run a small knife around edge of frittata & carefully slide onto a platter.