Potato Soup with ribs

1/4 cup unsalted butter 1 1/2 lbs yellow onions , thinly sliced (about 4 cups) 3 celery ribs , chopped salt crushed red pepper flakes fresh ground black[...]

2 1/2 lbs unpeeled small red potatoes , cut into 1-inch cubes 1 large onion , diced 3 celery ribs , diced 3 slices bacon , diced 8 cups milk 4 cups water 3[...]