In a slow cooker, I prefer to cook bean soup on HIGH because it ensures that the beans will become tender within a reasonable amount of time. You can cook this bean soup on LOW, but the cooking time becomes longer and more variable.
You can serve 15 bean soup with toppings such as hot sauce, sour cream or grated cheese.
Leftovers keep really well for up to 5 days. You can freeze the soup for up to 3 months.
Instant Pot Instructions
This recipe was tested in a 6-quart pressure cooker.
When using a pressure cooker, pre-soaking the beans is optional.
Step 1: In the Instant Pot, saute the onion, celery and carrot in olive oil until soft. Add the garlic and saute 30 seconds more.
Step 2: Add the beans, water, salt and parsley or thyme. (8 cups of water will make a brothy soup, 6 cups will make a thicker soup). If adding the optional ham shank or ham bone, add it now.
Step 3: Un-soaked beans can be cooked for 40 minutes, natural release. Soaked beans can be cooked for just 20 minutes, natural release.
Step 4: After the natural release, open the lid and stir in the spices listed in the ingredient list and add the spice packet that comes with the dried beans. Add the vinegar, and add salt to taste.
Step 5: If adding the optional frozen spinach and/or canned tomatoes, add now. If adding diced ham or slices of sausage, add it now (you can saute the sausage first, for more flavor).
Step 6: Let the soup simmer for another 5 minute or so until the added veggies and/or meat are warmed.