Crockpot Scalloped Potatoes

4 cups potatoes, sliced and peeled
1 (12 ounce) can evaporated milk
1 (10 3/4 ounce) can cream of celery soup
1 large onion
1/2 teaspoon salt
1/4 teaspoon pepper
1 cup chopped ham
2 tablespoons butter

Combine all ingredients except ham and mix well. Cover and cook on high for 1 hour. Add in ham. Reduce to low heat and cook for 6 hours longer or until potatoes are tender.
Makes 6-8 servings. (Use a 3 quart crockpot)