
Rinse beans and take out any stones or other matter. Put them in large pot covered by 8-10 cups of hot water. It doesn't have to be boiling, but should be quite hot. (Use a microwave or heat water in a kettle or on stove rather than use hot tap water.) Boil beans for 2 minutes, then turn off heat and let them soak for 1 hour.
While beans are soaking, heat the oil in a medium pan. Add the onion and gently sauté for about 10-12 minutes, until onion is soft and beginning to brown.
Once the onions are soft and beginning to brown, add the other ingredients except for the broth and water - the molasses, brown sugar, maple syrup, mustard, black pepper, vinegar, Worcestershire and soy sauces, and tomato paste and sesame oil if using. Mix the ingredients well. You might heat this mixture slightly in the pan before pouring it into the drained beans.
Preheat oven to 300° F/150° C Drain the beans and return them to the pot. Add the onions and other ingredients from the pan and mix. Add the hot vegetable broth and water if using, to cover. (Generally, the beans will take about 4 cups of liquid at this point) Bake, covered with the lid, for 4-5 hours. Check periodically, at least after 2 hours, and then every 45 minutes to 1 hour after that, adding more broth and/or water when necessary to keep beans in a loose sauce. If the mixture is very soupy at the end (last 30-45 minutes), you can turn the heat up to 350° F/180° C.
Once the beans are tender, but not mushy, take the pot out of the oven, uncover it. Then stir and taste for seasoning. You may want to add salt at this point. However, the soy sauce and vegetable broth may have provided enough salt. so let your taste buds be your guide. Continue cooking, uncovered, on the stove, under medium heat, stirring occasionally, until the sauce thickens and a crust forms on top, about 30-45 minutes.
Let the beans cool a bit, then refrigerate overnight or for a day before serving. Reheat in a microwave or on the stove. Once reheated, if necessary, add a bit more warm broth and/or water to loosen up the sauce.
Beans - Navy beans are traditional for this style of baked beans. But if you can't find them, or prefer another, use Great Northern or pinto beans.
Brown sugar - The difference between light and dark brown sugar is simply the amount of molasses. I like the molasses taste in my beans so I use dark. It's personal preference, so go with what you like.
Tomato paste or substitute - I like a complex taste that includes a bit of a tomato-ey undertone. The amount of tomato paste specified gives that result. Use a bit more, leave it out, or substitute another tomato-based ingredient if you prefer. If you use tomato sauce or ketchup, you'll want to use more than 1 teaspoon to get the same effect, as paste is more concentrated than sauce or ketchup.
Toasted sesame oil - To me, this umami-boost is unnecessary, but if you're a huge umami fan, then add it for a little extra oomph.
Liquid - broth and/or water - the broth gives these beans flavor complexity and I urge you to use at least 50% broth. But if you prefer your beans "straight up", ie with plain water, that's fine. Either way, make sure the liquid is at least hot to the touch when you add it, so you don't cool the beans down too much.