• Preheat oven to 400 degrees and line a 12-cup muffin tin with muffin liners. Set aside.

Topping

• 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.

Apples

• Mix apples with cinnamon, cloves, allspice and zest. Set aside.

Muffins

• 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. 

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.
• Enjoy!