Preheat the oven to 350 degrees.

In a large skillet, melt 1 tablespoon of the butter over medium high heat. Add the leeks and saute for 5-6 minutes or until wilted but not browned. Remove leeks from the pan and set aside.

In the same pan, melt the remaining butter over medium heat. Add the flour, salt, and pepper and whisk together until smooth. Cook for one minute. Slowly add the milk, whisking constantly. Bring the mixture to a boil. Cook, stirring constantly, for 2 minutes or until thickened.

Remove the pan from the heat and add 1 1/2 cups of Sargento® Chef Blends™ 4 State Cheddar® stirring until cheese is melted. Reserve the remaining cheese for the topping. Add the sliced potatoes, leeks, and bacon. Stir until thoroughly mixed being careful not to break the potato slices.

Transfer the mixture to a greased baking dish. Cover with foil and bake for 1 hour.

In a small bowl, combine the remaining cheese with the bread crumbs. Carefully remove the baking dish from the oven and evenly sprinkle the top with the bread crumbs and cheese mixture. Return to the oven and bake uncovered for an additional 30-40 minutes or until the potatoes are tender.