Step 1

Preheat oven to 350 degrees F. Line twelve 2 1/2-inch muffin cups with paper bake cups; coat inside of cups lightly with cooking spray. Set aside. Place the 2 cups oats in a food processor or blender; cover and process or blend until finely ground. Transfer ground oats to a large bowl. Stir in whole-wheat flour, sugar, baking powder, 3/4 teaspoon apple pie spice, baking soda and salt. Make a well in the center of the flour mixture; set aside.

Step 2

In a medium bowl whisk together buttermilk and eggs; whisk in banana, 2 tablespoons melted butter and vanilla. Add buttermilk mixture all at once to flour mixture; stir just until moistened (batter should be lumpy). Spoon batter into prepared muffin cups, filling each about three-fourths full.

Step 3

For topping, in a small bowl stir together 1/4 cup oats and 1/2 teaspoon apple pie spice. Using a pastry blender, cut in 1 Tablespoon butter until mixture resembles coarse crumbs. Sprinkle the oat mixture on top of muffin batter.

Step 4

Bake for 20 to 22 minutes or until a toothpick inserted in centers comes out clean. Cool in muffin cups on a wire rack for 5 minutes. Remove muffins from muffin cups. Serve warm.