Begin by peeling, coring, and slicing or chopping the apples to your preferred size—thin slices work well for pies, while chunks are great for crisps or fillings.

In a medium saucepan over medium heat, melt the butter along with the ground cinnamon until fragrant. Add the prepared apples, granulated sugar, and 3 tablespoons of water to the pan. Stir to combine everything well, then cover and cook, stirring occasionally, for 4 to 6 minutes or until the apples begin to soften slightly but still hold their shape.

In a small bowl, whisk together the cornstarch and 2 tablespoons of water to create a smooth slurry. Slowly pour the mixture into the pan while stirring to prevent any lumps. Continue cooking for a few more minutes, stirring gently, until the apples are tender (but not mushy) and the sauce has thickened to a rich, glossy consistency.

Allow the filling to bubble for about 1 minute to ensure the cornstarch activates fully. Remove from heat and let cool before using in pies, pastries, or as a warm topping.