Preheat oven to 160ºC .
Cover the beans with dozen cups cold water. Let soak overnight. In the morning pour the whole thing in a large saucepan. Add 1 tsp soda and more cold water to cover the beans if necessary. Bring to a boil, uncovered, then boil until some of the skins come off when you blow on the beans.
Line a bean pot with the sliced pork, then pour in the beans and their water. Roll the onion in the dry mustard until all of the mustard sticks to it, then bury it in the middle of the beans. Pour the maple syrup and coarse salt on top.
Bake 4-5 hours in your preheated oven. In the last hour of cooking, cover the beans with whole apples, placed as close together as possible. Cream together the sugar and butter, then spread the mixture on top of the apples. This forms a most delicious topping when the beans are baked. Pour the rum on top just before serving.