Rehydrate your potatoes for about half an hour, drain well, heat skillet with butter or bacon fat and put a big spoonful on the skillet. Shape into a patty and let it set till it's golden brown before you turn them. Add more butter if you need to when you turn them and brown the second side like the first. That will make you some very nice patties. If you want O'Brien Potatoes, add some onions and bell peppers to the mix and fry like you would regular fried potatoes and brown, turn, brown, turn etc.
My DH loves his dehydrated taters. they don't bother him like fresh do.
Mushroom