In a large bowl, combine buttermilk, oats, eggs, sugar, apple, and your choice of optional flavor additions below. Soak the mixture overnight so it will be ready at breakfast, or soak the oats for a few hours so that the oats will absorb the milk.
Combine flours, baking soda, baking powder and salt. Sift. Set aside until ready to mix.
In the morning, or whenever you're ready to mix the batter, preheat oven to 375°F. Grease a 12 ct. muffin tin very well, or line it with paper muffin. Fold sifted dry ingredients gently into buttermilk mixture until just combined. Do not over-mix.
Fill muffin tins (easy with an ice cream scoop). Bake 25 - 30 minutes, until brown and fragrant. Loosen from tins immediately. These muffins keep well for several days, and can be frozen.
Flavor additions: 1 cup fresh blueberries, plus grated zest of 1 orange or lemon, ⅔ cup raisins and ½ cup chopped walnuts, 1 cup fresh cranberries (ADD ⅓ cup white sugar), ⅔ cup dried cherries or cranberries & ½ cup chopped pecans. -- You get the idea, make up your own combos!