Preheat the oven to 250°F.
Fill a medium pot with just enough water to cover the beans. Add 2 tablespoons salt, bring to a boil, and reduce the heat so the water simmers. Cook the beans for 25 minutes, just long enough to soften them.
As the beans simmer, heat a large skillet, preferably cast iron, over medium heat. Fry the salt pork, turning to brown all sides, 5 to 6 minutes total.
Transfer the pork to a plate, leaving the rendered fat in the pan. Add the onion to the pan with a pinch of salt and cook to soften, about 5 minutes.
put the salt pork and the onion in a large bowl. Drain the beans and add them to the bowl. Stir in the ketchup, molasses, maple syrup, vinegar, mustard, brown sugar, 1 teaspoon salt, and a few twists of pepper.
Transfer the mixture to a bean pot or large dutch oven. Pour in just enough boiling water to cover the beans, stir to combine, and bake for 5 to 6 hours, until the beans are tender and sauce has reduced. Check occasionally to see if you need to add more boiling water so the beans don't dry out.
Season to taste and serve with a drizzle of maple syrup.
