Homemade Apple Cinnamon Muffins with a Crumb Cake Topping are soft and fluffy, full of sweet cinnamon apples, and have a cinnamon glaze drizzled on top.
Preheat oven to 400 degrees and line a 12-cup muffin tin with muffin liners. Set aside.
Mix brown sugar, flour and rolled oats together. With a pastry cutter, fork or masher, cut butter into mixture and work together until the mixture resembles coarse crumbs. Set aside.
Mix apples with cinnamon, cloves, allspice and zest. Set aside.
In a large bowl, mix flour, granulated sugar, brown sugar, baking powder, baking soda, salt and ground cinnamon together.
Make a well in the center of the ingredients, and add in the buttermilk, egg, canola oil and vanilla extract.* Mix until just combined.
Fold in the chopped apples, mixing until just combined.
Fill muffin cups with about 2/3 cup batter (this should make about 12-13 standard size muffins).
Generously sprinkle the oat topping into each muffin cup, pressing the crumb down into the batter.
Bake for about 15-16 minutes, or until muffins are lightly golden and a toothpick (or cake tester) comes out clean.
While the muffins are cooling, make the glaze.
Whisk powdered sugar and milk together, beginning with 3/4 cup of powdered sugar and 1 Tbsp of milk. If the glaze is too thin, add in the remaining 1/4 cup of powdered sugar (1 Tbsp at a time). If the glaze is too thick, drizzle in the remaining Tbsp of milk. Whisk in cinnamon (use a 1/4 tsp for a subtle cinnamon flavor; use 1/2 tsp for a robust cinnamon flavor).
Drizzle the glaze over each muffin.
*It's easy to over mix batter, which creates tough and dry muffins. By making a well in the dry ingredients and pouring the liquid into it, you minimize the amount of mixing because you are maximizing the contact of wet to dry ingredients.