I thought my relatives' cooking instructions were gone forever, but I discovered them, and the dish is more delicious than I remembered!

Preheat your oven to 325°F (165°C).
Drain and rinse the soaked beans. Place them in a large pot and cover with fresh water. Bring to a boil, then reduce heat and simmer for about 45 minutes, or until the beans are tender but not mushy.
In a large oven-safe pot or Dutch oven, combine the maple syrup, brown sugar, molasses, chopped onion, minced garlic, dry mustard, salt, and black pepper.
Drain the cooked beans and add them to the pot with the sauce mixture. Stir to coat the beans evenly.
Add 4 cups of water to the pot, ensuring the beans are submerged. Stir well.
Cover the pot and bake in the preheated oven for 2 to 3 hours, checking occasionally to ensure the beans remain covered with liquid. Add more water if necessary.
Remove the lid for the last 30 minutes of baking to allow the sauce to thicken and caramelize.
Once the beans are tender and the sauce is thick and glossy, remove from the oven and let cool slightly before serving.
Variations & Tips
For a smoky flavor, add a few slices of bacon or smoked sausage to the pot before baking. You can also experiment with different types of beans, such as pinto or kidney beans, for a varied texture. For a spicier kick, add a pinch of cayenne pepper or a dash of hot sauce to the sauce mixture. If you prefer a vegetarian version, use vegetable broth instead of water for added depth of flavor.