3/4 cup quick-cooking oats
1 1/2 cups well-shaken buttermilk, divided*
3/4 cup whole-wheat flour
1 1/2 teaspoons baking powder
3/4 teaspoon baking soda
1/2 teaspoon cinnamon
1/8 teaspoon grated nutmeg
1/2 teaspoon salt
1 large egg, lightly beaten*
2 tablespoons unsalted butter, melted
1 tablespoon packed brown sugar

Soak oats in 3/4 cup buttermilk 10 minutes. Meanwhile, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt in a large bowl. Stir egg, butter, brown sugar, remaining buttermilk, and oat mixture into dry ingredients until just combined.

Heat a griddle over medium heat until hot and lightly brush with oil. Working in batches, pour batter onto griddle and cook until bubbles appear on surface and undersides are golden-brown, about 1 minute. Flip with a spatula and cook other side, about 1 minute more. (Lightly oil griddle between batches.)