For the Apple Pie Filling

1. In a large saucepan over medium-high heat, heat chopped apples and butter together for about 5 minutes until the apples are soft and begin to turn slightly more brown in color. Mix consistently to ensure that the apples heat evenly.
2. Add light brown sugar and cinnamon to the apple mixture, and lower heat to medium-low. Heat for an additional 3-5 minutes until the apples are soft enough to break apart when you push down on them with a spoon. Stir as the mixture combines.
3. Remove the apple pie filling from the heat and let the mixture cool as you prepare the cookies. If baking or assembling later, allow the apple pie filling to cool before storing in an airtight container or covering with cling wrap, plastic wrap, or aluminum foil. Place the filling in the fridge for up to 6 days and heat for about 1 minute in the microwave before adding to the cookies.

For the Cinnamon Cookies

1. Preheat your oven to 350 degrees Fahrenheit and line baking sheets with parchment paper to ensure the cookies do not stick to your pans.
2. In a medium-sized bowl, whisk all purpose flour, baking soda, salt, and ground cinnamon together until combined.
3. In a large bowl with a hand mixer or in the bowl of your stand mixer that is fitted with a paddle attachment, beat room temperature butter, light brown sugar, and granulated sugar together on medium speed until smooth, fluffy in texture, and pale and shiny in color. This should take about 3 minutes of mixing.
4. Add eggs, one at a time, to the dough, beating thoroughly between each addition. Add vanilla extract, beating until smooth and fully incorporated. Use a spatula to scrape down the sides and bottom of the bowl, ensuring that all of the wet ingredients are combined.
5. Slowly, add the dry ingredients to your dough. Beat until smooth, but do not mix past when you see the dry ingredients disappear into the batter. 
6. Form the dough into 1 1/2-2 tablespoon sized balls, about 40-50g of dough per ball. Roll the dough balls in the mixture of granulated sugar and ground cinnamon if desired. Place the dough balls at least 2 inches apart on the parchment-lined baking sheets.
7. Use your thumb to make a well in the center of each cookie.
8. Bake the cookies for 10-14 minutes or until the tops are golden brown in color and the bottoms, when lifted with off the baking sheets with a spatula, are golden brown in color.
9. If desired, use your thumb to make the well deeper and more defined as needed. Allow the cookies to fully cool before filling and decorating.
10. After the cookies have cooled, fill each cookie with about 1 1/2 tablespoons (about 35g) of apple pie filling in the center of the cookies.

For the Glaze & Decoration

1. In a medium bowl, use a spoon to combine the milk, powdered sugar, and cinnamon to create the glaze.
2. Glaze should be thick. You should be able to easily lift your spoon from the bowl and have the glaze slowly but consistently fall off of the spoon. It should not look wet or runny at all. If the glaze is too thick to stir and does not easily fall off of a lifted spoon, add an extra teaspoon of milk until desired consistency is reached. If mixture is too thin, add powdered sugar by the tablespoon until desired consistency is reached.
3. Use a spoon, piping bag, parchment triangle, or Ziploc bag with the corner cut off to top the cookies with the glaze. Store at room temperature in an airtight container or tightly covered for up to a day or in the fridge for up to 5 days. Heat cookies in the microwave before serving if desired.