Peel and cut potatoes into bite-sized chunks, place in a large pot with 4 cups of water. Cover and boil for 15-20 minutes or until potatoes are soft all the way through then drain away water.
In a dutch oven over medium heat, sauté leeks in butter until softened. Add diced ham, stirring occasion. Cook until leeks are translucent and ham is lightly browned.
Whisk in flour and cook for 2-3 minutes to cook out the floury taste, whisking continuously. Slowly whisk in milk and continue stirring until thick. Turn down heat and simmer for 10 mins.