1. Pre-heat the oven to 375 degrees F. Boil the potatoes. Allow to cool slightly and dice. Place in a casserole dish.
2. Melt the butter in a saucepan. Whisk in the flour and cook for 5 minutes, stirring frequently. Whisk in the milk and cream. Reduce the heat and simmer for 20 minutes. Whisk in the cheese until blended.
3. Pour over the potatoes. Top with the breadcrumbs and bake for 25 minutes.