Place the chopped apples in a large pot, preferably one with a heavy bottom. Sprinkle cinnamon on top, if using, and pour in the water.
Cook on medium-high for 15 minutes, or until the apples have become very soft.
Puree the apples into apple sauce using an immersion blender, food processor, blender, or food mill, being mindful of how hot the apples are.
Serve immediately, refrigerate for up to 7 days, or freeze for 6-9 months (see below for freezing instructions).
Tip: Any apple sauce that you won't use in the next week or so can and should be frozen (or canned). To freeze it, decant the sauce into containers or freezer bags, leaving some room for expansion. Leave the containers open/uncovered on your counter until the sauce has cooled to room temperature, close up, and then freeze. It will safely last 6-9 months in the freezer.