Maple Baked Beans

My mom makes the best baked beans.  This is her recipe that she found in Feeding the Healthy Vegetarian Family by Ken Haedrich. 

1 pound dried Great Northern beans
1/4 cup safflower oil
1 cup chopped onions
1 green bell pepper, finely chopped
1 celery rib, finely chopped
2 garlic cloves, minced
1/2 cup maple syrup
1/2 cup canned tomato puree
3 tablespoons apple cider vinegar
2 tablespoons blackstrap molasses
2 tablespoons Dijon mustard
1 1/4 teaspoon salt
1 bay leaf
1/4 cup chopped fresh parsley (optional)
freshly ground pepper to taste

Pick the beans over and rinse well.  Put the beans in a large pot and cover with about 3 inches of water.  Bring to a boil, then boil uncovered for 2 minutes.  Remove from heat and cover.  Let the beans soak for an hour, then drain. 

Cover the beans generously with fresh water and bring to a boil.  Gently boil the beans, partially covered, for 1 to 1 1/2 hours, until the beans are tender but not mushy.  Drain the beans, but this time don't discard the cooking water. 

While the beans cook, heat the oil in a large skillet.  Add the onions, pepper, and celery and saute over medium-high heat for about 6 minutes.  Stir in the garlic, saute for 15 seconds more, then remove the skillet from heat.  Preheat the oven to 325 degrees and get out a large shallow casserole dish. 

Whisk together the remaining ingredients, adding 1 1/2 cups of the bean cooking water.  Transfer the beans, sauteed vegetables, and tomato liquid to the casserole and stir gently to blend.  Cover the casserole tightly with foil and bake the beans for 2 to 3 hours.  Check the progress of the beans every hour, stirring then and checking on the level of the liquid; if it is getting too low, stir in a bit more bean water.  When the beans are done, the liquid should be fairly thick and saucy.  Serve hot.