Drain the beans and place them in a large stockpot with enough fresh water to cover them. Add salt and bring the beans to a boil. Cover the pot, turn the flame down to medium-low and let cook for 1 full hour.
Preheat oven to 300° F and combine the sauce ingredients (listed above) together in a small bowl. Set the sauce aside until ready to use.
Reserve 4 cups of the cooking water from the beans before draining them. If there isn't enough water to measure 4 cups, you can just add tap water.
In a large dutch oven, heat the bacon grease or butter over a medium flame and add the onions, bell peppers and jalapeños. Sauté for 1-2 minutes, until the onions are clear. Add the sauce and 2 cups of the reserved water from the beans, stir and let everything simmer.
Add the beans to the dutch oven and stir until the beans are fully coated in sauce. Top the beans and sauce off with the remaining 2 cups of cooking water, stir one more time, and cover the dutch oven.
Transfer the dutch oven to the oven and bake for 2 hours. Stir the beans every 30-40 minutes or so. The beans should remain moist but you can add a small amount of boiling water to keep the beans from drying out, if needed. Once the 2 hours is up, uncover the beans and bake them for another 30 minutes.
Let the beans cool slightly before serving.
Notes
Feel free to adjust the amount of cayenne pepper or number of jalapeños, if you don't want your beans to be too spicy. Removing the seeds from the jalapeños is another way to cut down on the spice.