Rinse the beans well and pick them over. Discard any malformed beans or small stones you might find.
Transfer the beans to the slow cooker. Add 1 1/2 quarts of water to the ceramic insert.
Add the onion, carrot, celery, bay leaves, garlic, celery flakes, parsley sprigs, and freshly ground black pepper.
Cover and cook on LOW for 5 1/2 to 6 1/2 hours.
Add kosher salt, to taste.
Serve the beans over steamed or boiled rice; use them in salads, chili, stew, or soup; or mash them as a dip or a spread for crostini appetizers. You can use them in any recipe that calls for canned Great Northern beans.
Enjoy!
Notes
You can optionally plan for a quick-soak and some time at a simmer before you add the beans to the slow cooker. Do this for older beans or if you feel you frequently under-cook dried beans when you use them.
Store leftovers in an airtight container in the refrigerator for 4 or 5 days. Reheat them at medium power in the microwave or in a saucepan over medium heat on the stove. You can also enjoy them cold in a salad or dip.
Freeze leftover beans in recipe-portion or serving-size containers for later use. Let the beans cool thoroughly on the counter before you pack them into airtight containers, leaving about 1/2-inch of head space to allow for expansion. Reserve about 3/4- to 1-inch of headspace in narrow-mouth containers to allow for expansion. You can also freeze beans in zip-top freezer storage bags. For best quality, use them within three months.