In a large mixing bowl, combine the buttermilk, oats, flour, milk, butter, baking powder, baking soda, pinch of cinnamon, and nutmeg. Stir to gently combine, then set aside to rest for a few minutes. Combine the apple, apple juice, brown sugar, and remaining 1⁄8 teaspoon cinnamon in a small saucepan and bring to a simmer. Cook until the apple has softened and the liquid has thickened. Preheat the oven to 200°F. Heat a large nonstick or cast-iron skillet over medium heat. Adding a bit of butter or cooking spray before each round, scoop 1⁄4-cup portions of batter into the skillet and use a spatula to spread into thin, even circles. Cook until small bubbles form in the top of the batter, 2 to 3 minutes, then flip and cook for another 2 minutes. Keep pancakes warm in the oven while you finish cooking. Serve topped with the warm apples and a bit of confectioners' sugar, if you like.