Preheat the oven to 450oF. With the tinges of a fork, poke each potato 3 to 4 times. Place on a microwave-safe plate. Microwave on high 10 to 12 minutes until the potatoes feel soft when pressed with a dishtowel or oven mitt. Set aside to cool 4 to 5 minutes.
Slice the potatoes into 1?4-inch thick slices. In an 8×12-inch baking dish, layer half of the sliced potatoes. Sprinkle over half the onion slices, salt, paprika and black pepper. Sprinkle with half the flour and then top with half the cheese.
Repeat with remaining ingredients, add the milk, and cover with aluminum foil. Slide the dish into the oven and bake 15 minutes until the cheese is melted.
Remove the foil and bake and additional 5 to 10 minute until the top is lightly browned. Cool 5 minutes before serving.