1Preheat oven to 350 degrees F (175 degrees C). Generously grease muffin cups or line with paper liners.
2Combine oats, oat flour, cinnamon, allspice, baking soda, and salt in a large bowl. Add apples, yogurt, eggs, brown sugar, butter, and vanilla extract to oat mixture until batter is well mixed; fold in walnuts. Pour batter into the prepared muffin cups.
3Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 25 minutes.
Footnotes
Cook's Note:
Add 1 cup whole oats to food processor to make oat flour.