Preheat the oven to 350 degrees Fahrenheit (177 degrees Celsius). If using a glass dish, preheat to 375 F (191 C). Peel and thinly slice apples, and place in 8x8-inch buttered baking dish. To make the oatmeal mixture, combine in a bowl: cinnamon, brown and white sugars, flour, salt and oats. Mix 1/3 cup softened butter into the oatmeal mixture with your fingers. Spread the oatmeal mixture on top of apples and press down slightly. Bake until the top is a little brown and the apples are tender, about 30 minutes. Let cool for 15 minutes and serve warm. Top with vanilla ice cream, if desired.