Whisk in the sugar, brown sugar, and cinnamon until smooth and well blended.
Turn heat down to low and add in the apples.
Cook over low heat stirring often until apples are softened, about 10 to 15 minutes.
Simmer a little longer to thicken up the syrup but don't overcook the apples.
Notes
Storage:Place cooled leftovers into an airtight container or plastic bag and refrigerate for four to five days.Freeze for up to 3 months.Tips:
Use a combination of apple varieties for the very best flavor.
For best results, try to cut the apples as evenly as possible so that they all cook at the same rate. It helps to use a very sharp knife or an apple slicer.
Let the apples come to room temperature (if they were cold) so that they don't reduce the temperature of the simmering, sticky caramel sauce too drastically.
Watch the butter, sugar, and apple mixtures carefully throughout the cooking process so that they don't burn. As trusty as an old cast iron skillet is, it can get too hot as soon as you turn your back!
If your caramel sauce becomes too thick (especially after reheating) you can loosen it up with a splash of apple juice or apple cider.