peel and slice thin enough potatoes to measure about 6 cups, place sliced potatoes in a bowl of iced water so they will not brown while you make the cheese sauce

in pan on the stove over med heat melt butter, stir in the onion powder, turn down heat to med-low and stir in flour and pepper, stirring constantly, until it is bubbly, remove from heat

stir in milk and 2&1/2 cups of shredded cheese, heat this to a boil over med-low to med heat stirring constantly, once it reaches a boil, boil and stir for 1 min, then take off heat

with non stick cooking spray, spray a 9x13baking dish, spread half the potatoes in the pan, then spread half of the remaining cheddar cheese over potatoes, now pour all of cheese sauce over potatoes, u might have to let cheese sauce work its way down, sprinkle with remaining cheese on top and bake uncovered in the oven at 325*F for 1&1/2 hrs to1 hr 45 min, when knife or fork is stuck in it should slide in easy, if top gets to brown, cover with foil, but try not to if u can