Note: Although potatoes may be sliced using a sharp slicing knife, it is best to use a mandolin to achieve the thinness required. It is also imperative to line your baking pan with parchment paper prior to baking. Preheat oven to 350 degrees F. In a mixing bowl, combine eggs and whipping cream. Whip well and set aside. Using a mandolin, slice sweet potatoes either cross or long ways. Continue with baking potatoes, working quickly to prevent them from oxidizing. Place the potatoes in separate bowls and season generously with salt, black pepper and nutmeg. Using your hands, rub the potatoes gently to blend the seasonings and coat the potatoes well with their natural starch. Line a 9" x 13" baking dish with parchment paper and coat with nonstick cooking spray. Place a layer of sweet potato slices on the parchment paper and sprinkle evenly with 1 tablespoon each of Parmesan cheese and Romano cheese. Repeat with a layer of white potatoes then continue layering to 1/4 inch from the top of the baking pan, sprinkling cheeses between each layer. Pour cream mixture over potatoes and allow to soak through all layers. Top with remaining cheese. Cover with aluminum foil and bake 1and 1/2 hours or until potatoes are tender and custard is set. Uncover and bake until lightly browned. Remove from oven and allow to cool slightly. Place a layer of foil or cling wrap over the top of the baking pan. Place a cutting board or baking tray on top of the potatoes that fits snuggly inside the perimeter of the pan. Place a cast iron skillet or other object to apply weight gently to the top of the potatoes, pressing them firmly overnight. Allow to cool in the refrigerator a minimum of 12 hours. When ready to serve, turn potatoes onto a cutting board and remove parchment paper. Cut into squares, triangles or circles as desired. Microwave or reheat in oven at 350 degrees for 15 minutes before serving.