Preheat oven to 400°F. Cook the potatoes in boiling water until tender. Drain. In a skillet, fry bacon until crisp and drain well on paper towels.
Trim leeks so that you have the white part and a small amount of green. Wash well, and slice thinly. Add leeks to skillet and sauté over medium heat until soft.
Slice the boiled potatoes, and arrange half in the bottom of a pie plate. Season with salt and pepper. Layer with bacon, leeks and one half of the cheese. Cover with remaining with remaining potatoes and season again. Sprinkle with remaining cheese. Bake for 30 minutes or until top is browned and cheese is melted.