Sort through the dried white beans, removing any shriveled or debris, then rinse them thoroughly under cold water. Place the beans in a large bowl, cover with water, and soak overnight, or do a quick soak by boiling for 5 minutes and letting sit for an hour.
Drain the soaked beans and transfer them to your slow cooker. Pour in the vegetable broth, then add the diced onion, minced garlic, sprigs of fresh thyme, and bay leaf. Season with a teaspoon of salt and a few cracks of black pepper.
Cover the slow cooker and set it to low heat. Let the soup cook for 6 to 8 hours, until the beans are tender and breaking down slightly, filling your kitchen with a cozy aroma.
Once cooked, turn off the slow cooker. Remove and discard the bay leaf and thyme sprigs. Use a potato masher or an immersion blender to mash some of the beans directly in the pot, creating a thicker, creamier texture. For a smoother soup, blend all or part of it.
Taste the soup and adjust the seasoning with more salt and pepper as needed. Drizzle with a tablespoon of olive oil for extra richness and shine, if desired.
Serve the soup hot, garnished with fresh herbs or a drizzle of olive oil. Enjoy with crusty bread or a side salad for a complete, comforting meal.
