Combine the first five ingredients. In a 1-pint glass jar, layer 3/4 cup flour, oats, sugar mixture and remaining flour. Cover and store in a cool, dry place for up to 6 months. Yield: 1 batch (about 2 cups total).
To prepare muffins: Preheat oven to 375°. Combine egg, applesauce, butter and vanilla. Stir in muffin mix just until moistened. Fill greased muffin cups three-fourths full. Sprinkle with sugar. Bake until a toothpick comes out clean, 15-20 minutes. Cool 5 minutes before removing from pan to a wire rack.