Cut the green parts off the leeks. Cut the roots off making sure the leeks sections are still connected at the very bottom.
Run the leeks under water to remove any dirt or debris.
In a large saucepan, melt the butter over medium heat, then add the leeks with a heavy pinch of kosher salt.
Cook the leeks for 5 mintues. Turn the heat down if the leeks are starting to get too brown.
Decrease the heat to just above low and cook for 20 mintues or until leeks are tender. Stir occasionally, and check to make sure they don't burn.
Add the potatoes and broth to the pan. Increase heat to bring just to a boil.
Decrease the heat to low and simmer the potatoes for 45 minutes. Increase or decrease the heat to keep the potatoes at a simmer.
Remove the pot from the heat. If you want a smooth soup puree it completely. If you want a more chunky soup, remove some of the soup to a bowl, puree it and add it back in.
Stir in the heavy cream, buttermilk, bacon, white pepper. Taste and then add more salt to taste. Serve.