"The oatmeal and big apple slices in this batter means that I'm never able to make nice, round, smooth-edged pancakes with it. Nevertheless, I love the rustic, hearty textures and rich flavors of this pancake."
In a Pyrex measuring cup or other microwaveable bowl, microwave milk and butter, if using, until the butter is melted and the milk is hot, about 45 seconds.
Put oatmeal in a large mixing bowl. Pour hot milk mixture over oatmeal and let stand for 10 minutes.
Meanwhile, cut the apple in quarters, remove core, and slice quarters thinly. Cut apple slices in half if the apple is tall. Toss apple slices in cinnamon.
After 10 minutes, add to the oatmeal mixture: eggs, 1/4 cup of the flour, baking powder, sugar, salt, and oil, if using. Mix thoroughly. Stir in apple slices. Sprinkle last tablespoon of flour over pancake batter and stir.
Heat a nonstick pan over medium heat. Add a little oil or butter to the pan and tilt pan to cover bottom.
Using a 1/4 cup measure, ladle a slightly heaping quarter cup of batter into the hot pan. Cook the pancake until bubbles cover its surface, the edges are slightly dry and shiny, and the bottom is browned. Flip pancake with a spatula and cook top until it is browned.