1. Preheat the oven to 350 degrees F and line a muffin pan with muffin papers. 

   Tip: To help prevent the cupcake liners from sticking to the muffins, spray the liners lightly with nonstick spray before adding the batter. 

Crumb Topping

1. In a small bowl, whisk the flour, sugar, and ground cinnamon. Pour the melted butter slowly over the flour mixture, while slowly mixing. Mix until most of the mixture is crumbly. Be careful not to overmix, otherwise, it will become dough. Place in the fridge to chill, until the muffin batter is ready.
   35 grams all-purpose flour, 50 grams white sugar, 1 gram ground cinnamon, 42 grams unsalted butter, melted

Dry Ingredients

1. In a large bowl, whisk 245 grams (1 3/4 cups) flour, baking powder, baking soda, salt, and 4 grams (2 teaspoons) cinnamon. Set to the side.
   251 grams all-purpose flour, divided, 6 grams baking powder, 3 grams baking soda, 3 grams salt, 5 grams ground cinnamon, divided

Wet Ingredients

1. In a bowl of a stand mixer with the paddle attachment, mix the sugars and oil until combined. Add the eggs, one at a time. Remember to scrape the sides of the bowl with a spatula when needed.
   100 grams white sugar, 110 grams light brown sugar, 100 grams neutral oil, 100 grams eggs, room temperature
2. Add the sourdough discard, milk, and vanilla extract, and mix. It may start to curdle, but that's okay!
   60 grams milk, 120 grams sourdough discard, 6 grams vanilla extract

Combine

1. Add the flour mixture to the wet ingredients and mix on low until the dry ingredients are just combined. 
2. Peel and dice the apples. In a small bowl, add the apples, 6 grams (2 teaspoons) flour, and 1 gram (1/2 teaspoon) of cinnamon, and mix. This coating helps the apples from sinking to the bottom of the muffin.
   2 cups peeled and diced apples
3. Carefully fold the apples into the muffin batter.

Bake

1. Divide the muffin batter evenly into 16 lined muffin pan and fill 3/4 of the way full. Top with a portion of the crumble topping.
2. Bake the Sourdough Apple Cinnamon Muffins for 17-18 minutes. The muffins are done when the tops are golden brown and a toothpick comes out clean. 
3. Remove the muffins from the oven. Keep the muffins in the tin for 5 minutes, then place on a wire rack to cool completely. Enjoy!