Preheat your oven to 350°F (175°C). Make sure the oven is fully heated to ensure even baking. While it’s warming up, grease a 12 count muffin tin and set it aside for later.
In a medium bowl, combine the all purpose flour, white whole wheat flour, salt, ground cinnamon, and baking powder. Mix these dry ingredients together thoroughly to ensure an even distribution of the leavening agent.
In a large mixing bowl, whisk together the melted coconut oil, light brown sugar, eggs, cooked plain oatmeal, and unsweetened applesauce. This mixture should be smooth and well combined, providing the base for your muffins.
Now, gradually add the dry ingredients to the wet ingredients. Stir gently until just combined. Be careful not to overmix; this will help keep your muffins tender.
Fold in the finely chopped apple until evenly distributed throughout the batter, adding bursts of flavor in every bite.
Next, divide the batter evenly between the 12 muffin cups. I find that using a spring-loaded cookie scoop makes this task much easier and cleaner!
In a separate bowl, prepare the streusel topping. Combine the all purpose flour, old fashioned oats, brown sugar, chopped walnuts, and ground cinnamon. Mix these ingredients well.
Add the cold unsalted butter pieces into the streusel mixture. Using your fingers, work the butter into the dry ingredients until it resembles wet sand that clumps together when pressed.
Sprinkle the streusel evenly over the batter in the muffin cups, ensuring each muffin gets a delicious crunchy topping.
Bake in the preheated oven for 13 to 15 minutes or until a toothpick inserted into the center comes out clean. Keep an eye on them, as baking times may vary depending on your oven.
Once baked, remove the muffins from the oven and let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
