Slice potatoes lengthwise about 1/16 inch thick. Mix Together the Gruyere, mozzarella, and cheddar cheese. Place a layer of potatoes in the bottom of the baking pan, then top with a mixture shredded cheeses and add a pinch of salt and pepper. Repeat this process until pan is filled to about 1 inch from the top. Pour liquid into the pan.
Press the potatoes and cheese down in the pan just to compact little. Cover with the parchment paper and foil and bake for 2 hours on the top rack of the oven.
Remove the pan from the oven and reduce the heat to 200 degrees. Sprinkle breadcrumbs on top of potatoes; re-cover and rotate the pan as you return it to the oven. Bake for another 20 to 30 minutes or until potatoes are fork tender and the breadcrumbs are golden brown.