This recipe is originally from Cooking Light September 2014, but we made some modifications. Here is a link to original recipe on Cooking Light’s website. When Mom made it she used extra apples and more streusel for the topping.
Preheat oven to 400°. Prepare streusel by combining ingredients in a bowl; set aside. To prepare muffins, combine flours, cinnamon, baking powder, baking soda, and salt in a medium bowl. Combine buttermilk, 1/2 cup sugar, oil, 1 tablespoon melted butter, and egg in a bowl. Add buttermilk mixture to flour mixture, stirring just until combined. Fold in apple. Divide batter among 12 paper-lined muffin cups; top evenly with streusel. Bake at 400° for 16 minutes or until a wooden pick inserted in the center comes out with moist crumbs clinging. Cool in pan 5 minutes. Remove from pan; cool completely. Combine powdered sugar, syrup, and 1/2 teaspoon water in a bowl; stir until smooth. Drizzle evenly over muffins.