Rinse off your apples, then peel them and dice them into ~1" squares.
Add the diced apples, lemon juice, brown sugar, apple pie spice, cinnamon, and butter to a large saucepan. Stir all of the ingredients around so that the apples are evenly coated, then place over medium heat.
Bring the apple mixture to a simmer and simmer for 5-10 minutes, stirring occasionally, until the apples have softened a little bit.
Once the apples have softened, make the corn starch slurry in a small bowl by whisking together the corn starch and water until you have a smooth mixture. Slowly pour the paste into your apple mixture while stirring. Stir continuously until the mixture thickens, then remove it from the heat.
Store the apple pie filling in an airtight container in the fridge. Enjoy with your favorite fall bakes!