TWO-POTATOES ANNA

Steps:

• Position a rack in the upper third of the oven and preheat to 450 degrees F. Peel the sweet potatoes and slice into 1/8-inch-thick rounds (use a mandoline if you have one). Peel half of the russet potatoes and slice into 1/8-inch-thick rounds. (Do not rinse-you'll need the starch for the dish to set.)
• Coat the bottom of a 10-inch nonstick ovenproof skillet with 4 tablespoons melted butter. Starting in the center of the skillet, arrange a layer of russet potato slices in concentric circles, slightly overlapping them. Sprinkle with a pinch of salt and some of the rosemary leaves.
• Set the skillet over medium heat. Working quickly, add the remaining sliced russets in 2 more layers, then the sliced sweet potatoes in 2 layers, sprinkling lightly with more salt and rosemary between layers. (Check to make sure the bottom is browning evenly; adjust the heat as needed.) Drizzle with 4 tablespoons melted butter. Peel and thinly slice the remaining russet potatoes and add them to the skillet in 2 or 3 more layers, lightly seasoning each layer with salt and rosemary. Drizzle with the remaining 4 tablespoons melted butter.
• When the potatoes are golden brown on the bottom, transfer the skillet to the oven and bake until the potatoes soften slightly, about 30 minutes. Remove from the oven; center the bottom of a 9-inch cake pan on the surface of the potatoes and press firmly a few times to help the layers stick together. Remove the cake pan and return the skillet to the oven; bake until the potatoes are tender and the top is golden brown, about 20 more minutes.
• Let the potatoes cool 5 minutes in the skillet, then run a small knife around the edge to loosen. Set an inverted serving plate on top of the skillet and carefully flip the potatoes onto the plate. Season with salt and pepper.