Preheat oven to 350°. Prepare a 1½ - 2 quart baking dish by buttering the dish generously (I use cooking spray). In a double boiler, combine butter, milk, flour, onion, salt and pepper. Cook on low heat until it begins to thicken, stirring constantly with a whisk. Add 1/2 of your cheese and stir until cheese melts. Remove pan from heat and add parsley to your taste. While you are cooking this, in another saucepan add sliced potatoes and cover with chicken broth. Bring to a slow boil and cook slowly until they are about ½ done, no more, (about 5 - 7 minutes). Drain potatoes and place a layer of potatoes and a layer of cheese sauce, repeat. Reserve the rest of the cheese until later. Place potatoes in oven and bake for approximately 20 minutes until potatoes are tender and sauce is bubbly. Remove from oven and place remainder of cheddar cheese on top of potatoes. Return potatoes to oven for about 5 minutes until cheese is melted.