Add the navy beans to a pot and cover with two inches of water. Bring to a rolling boil, then remove from the heat, cover, and let soak for 1 hour.Drain the soaked beans, then add to the slow cooker along with the onion and garlic.* Add the vegetable broth and mix.Mix together all the remaining ingredients except the salt, cornstarch, and 1 Tbsp water. Mix well, then pour into the slow cooker and mix to combine.Cook on high for 7-8 hours, until beans are soft and the liquid has thickened a bit.Mix the cornstarch with the water, then add to the pot of beans and stir. Let sit about 5 minutes to thicken a bit before serving.