Cook's Note: The potatoes need to sit overnight in the refrigerator, so plan ahead.

Place potatoes in large pot of cold water to cover and add 4 tablespoons of salt to pot. Slowly bring to a boil and then reduce the heat and simmer until tender. Drain and let cool. Refrigerate potatoes overnight.

The following day, peel potatoes and grate into a bowl. Season, to taste, with salt and pepper and set aside. Heat 2 tablespoons of clarified butter in a medium saute pan over medium-high heat. Add 1 tablespoon of the unsalted butter and melt. Add leeks and saute until tender, about 5 minutes. Add crumbled bacon and set aside.

For the first Rosti:

Preheat the oven to 200 degrees F.

Add half of the remaining clarified butter and unsalted butter to a small or medium non-stick saute pan and heat over medium-high heat. Add 1/4 of the potatoes and 1/2 the leeks and spread evenly over the top. Cover evenly with 1/4 more of the potatoes. Brown the potatoes for about 5 minutes and then place a plate over the top. Flip the potatoes over, and slide them back into the pan. Brown for another 5 minutes. Sprinkle 1/2 of the Gruyere over the top and melt. Remove from the pan and place in the oven to keep warm.

For the second Rosti:

Add remaining clarified butter and unsalted butter to the saute pan. Repeat the process with the remaining potatoes, leeks, and Gruyere. Serve immediately.