Preheat the oven to 350℉/176℃. Grease a muffin tin well and set aside. Chop the apple into small cubes (see photo in step 4 above for reference) and set aside.
1 apple
In a bowl, add the oats, flour, baking soda, baking powder, cinnamon, cloves, and salt. Stir to combine and set aside.
3 cups rolled oats, 1/2 cup all-purpose flour, 1/2 tsp baking soda, 1 tsp cinnamon, 1/8 tsp cloves, 1/4 tsp salt
In another large bowl, add the brown sugar, applesauce, milk, eggs, and vanilla. Whisk together for a minute or so until smooth and well combined.
2 large eggs, 1 tbsp vanilla, 1 cup unsweetened applesauce, 1 cup milk, 1/4 cup dark brown sugar
Add the dry and wet ingredients together. With a spatula, gently mix just until a liquid-y batter forms. Do not over-mix.
Mix in the chopped apples and evenly distribute them - do not over-mix.
1 apple
Divide the batter evenly between the 12 cups - make sure to scoop equal parts of the liquid and the oats/apples. Fill all the way to the top. Sprinkle cinnamon sugar on top (optional).
Bake for 30-40 minutes or until a toothpick inserted in the middle comes out clean. Allow to cool, then gently run a knife around the edges of each cup and pop them out. Enjoy!