put beans in large bowl and cover with 3 times their volume of cold water. soak overnight in cool place

drain beans and transfer to large pot or dutch oven.

add 10 cups water and ham

bring to simmer over medium heat, then reduce heat to low and cook until beans are tender about 1 hour and 30 minutes

transfer ham to plate to cool slightly, then remove from bone and dice meat

return meat to pot

meanwhile cover the potatoes with water in saucepan and season with salt

bring to boil over medium high , then reduce heat and simmer until potato is fork tender, 20 or 25 minutes

drain the potato, transfer to bowl with the milk and mash until smooth

add mashed potato to bean soup and stir until combined

with melted butter in large skillet over medium heat add onion, celery garlic and parsley cooking until vegetables are translucent

then add vegetable mixture to soup, reduce heat to low and cook 1 hour adding up to 2 more cups water if too thick

season with salt and pepper

Alternative.... use 1 to 2 cups mashed potatoes and skip using russet potato