Put the beans to soak in an excess of cold water. They swell up a lot.
Prepare a garlic paste by mixing finely chopped garlic with bacon fat with the back of a spoon.
Remove the best meat from the hock and put it aside.
Prepare the stock by boiling the pork hock, onion, carrot, leak, garlic paste, thyme and bay leaf for 3 hours in enough water to cover the hock.
Strain the beans with a large colinder.
Add fresh water to the beans and boil for 5 minutes while skimming and discarding the froth which forms.
Strain the beans and then bring to the boil again with the stock. Add the salt and tomato paste. (Check that the stock is not salty already from the pork hock - if it is don't add salt). Simmer for 60 to 90 minutes.
Dice and brown the saved hock pieces, the duck and the sausage in a frying pan in duck fat.
Mix the diced meat and duck with the beans in a casserole pot, place the kransky sausage on top and sprinkle with black pepper.
Place the casserole in the oven and cook for 2 hours at 180 deg C without a lid. Push down the crust from time to time with a wooden spoon. Add more stock or water if the beans look like they are drying out. (It can dry out very rapidly towards the end so be careful.)
Serve piping hot straight from the oven. Each person is served a piece of duck and a sausage with tongs and then beans with a serving spoon or ladle.
Serves four but can be stretched to 6 or 7 if a large enough casserole can be found. The only expensive ingredient is the duck. This can be ommitted and it is still a great dish although it lacks a certain je ne c'est quoi without it.