Rinse the beans in a large colander, sorting out any discolored beans,
In a large pot over high heat, bring the water and stock to a boil. Add the beans and simmer for 5-10 minutes. Remove pot from heat and allow beans to soak for 90 minutes.
After soaking, return the pot to high heat and add the ham hock, carrots, celery, onion, garlic, mustard powder and bay leaves.
Stir well and bring to a boil. Reduce heat to low and simmer, covered, for 1.5 to 2 more hours, stirring occasionally. Uncovered and remove ham hock and bay leaves.
Stir in chopped ham and rosemary. Season with salt and pepper, to taste. Simmer for an additional 20-30 more minutes.