Step 1

Preheat the oven to 400 degrees F. Scrub the potatoes and place directly on the rack in the oven. Bake at 400 degrees F for 45 minutes or until fork-tender. Remove from the oven and let cool for 30 minutes. Reduce the oven temperature to 300 degrees F. Grease a 9x13 baking dish. While the potatoes are baking, heat the milk in a saucepan over medium heat. Do not let it boil. Melt the butter in a large saucepan over medium heat. Whisk in the flour and mix until smooth. Cook for 2 minutes, stirring constantly, until the mixture is just bubbly. Do not let it brown. While stirring, very slowly add the warm milk to the flour mixture. Bring the sauce to a simmer then reduce the heat and cook, stirring frequently, until thick, about 6-7 minutes. When the potatoes are cooled, slice them into 1/2-inch thick slices. Add the potatoes to the sauce along with the salt, pepper, Mozzarella, and Colby cheeses. Mix gently then transfer the mixture to the prepared baking dish. Cover the dish with foil and place in the oven. Bake at 300 degrees F for 1 hour or until bubbly and heated through. Remove the foil and let bake for 5-10 more minutes or until the cheese sauce has browned slightly.

Step 2

Preheat the oven to 400 degrees F. Scrub the potatoes and place directly on the rack in the oven. Bake at 400 degrees F for 45 minutes or until fork-tender. Remove from the oven and let cool for 30 minutes. Reduce the oven temperature to 300 degrees F. Grease a 9x13 baking dish. While the potatoes are baking, heat the milk in a saucepan over medium heat. Do not let it boil. Melt the butter in a large saucepan over medium heat. Whisk in the flour and mix until smooth. Cook for 2 minutes, stirring constantly, until the mixture is just bubbly. Do not let it brown. While stirring, very slowly add the warm milk to the flour mixture. Bring the sauce to a simmer then reduce the heat and cook, stirring frequently, until thick, about 6-7 minutes. When the potatoes are cooled, slice them into 1/2-inch thick slices. Add the potatoes to the sauce along with the salt, pepper, Mozzarella, and Colby cheeses. Mix gently then transfer the mixture to the prepared baking dish. Cover the dish with foil and place in the oven. Bake at 300 degrees F for 1 hour or until bubbly and heated through. Remove the foil and let bake for 5-10 more minutes or until the cheese sauce has browned slightly.