Preparation

• Preheat your oven to 375°F. Line a 12 count muffin tin with paper liners, and set aside.
• Make the streusel topping: In a medium bowl, combine all of the streusel ingredients (flour, sugar, cinnamon, and butter). Using a fork or pastry cutter, mash together until you're left with a crumbly mixture that sticks together when you pinch it with your fingers. Cover and set aside in your fridge until ready to use.
• Make the apple layer: In a medium bowl, combine all ingredients for the apple layer (apples, sugar, and cinnamon). Toss together to coat the apples in the sugar and cinnamon, and set aside to prep the muffin batter.
• Make the muffin batter: In a large bowl, combine flour, sugar, baking powder, cinnamon, and salt. Whisk together, then add in your butter. Cut the butter into the dry ingredients using a fork or pastry cutter until the mixture resembles coarse crumbs.
• Add the eggs, milk, vegetable oil, and vanilla to the flour / butter mixture. Whisk together until well combined. A few clumps in the batter are totally normal.
• Layer the muffins: Scoop the muffin batter into your prepared muffin tin cups, filling each cup a little over halfway full with the batter. Top each cup with a bit of the diced apple layer (if the apples have let out any liquid - which they usually will do - drain as much out as you can before topping the muffins). Top each muffin with your streusel topping.
• Bake the muffins in the center of your preheated 375°F oven for 15 to 20 minutes, or until a skewer inserted into the center of a muffin comes out clean of any batter.
• Cool the muffins in your muffin tin for about 10 minutes, then transfer onto a wire rack and set aside to cool completely. Serve plain or topped with a simple powdered sugar icing!