Place oats in a small bowl, pour in buttermilk. Let sit for two hours at room temperature.
Preheat oven to 375 degrees F (190 degrees C). Grease 12 muffin cups or line with paper muffin liners.
In a large bowl, stir together whole wheat flour, baking powder, baking soda and brown sugar. Stir in oat/buttermilk mixture, applesauce and egg; mix well. Pour batter into prepared muffin cups.
Bake in preheated oven for 30 minutes, until a toothpick inserted into center of muffin comes out clean.