Preheat the oven to 350°F. Line a 9x9-inch pan with parchment paper and grease any exposed areas.

Combine dry ingredients for the base/topping, mixing well. Add the softened butter, several tablespoons at a time, mixing it together, until crumbles form.

Reserve about ⅓ of the mixture for the topping and press the rest of the mixture into the bottom of the prepared pan. Bake for 15 minutes, then remove and set aside at room temp until ready to fill.

Peel, core and thinly slice the apples into evenly sized pieces. Transfer the apples to a large high-sided skillet. Sprinkle the apples with cinnamon and cornstarch. Mix to coat the apples as evenly as possible.

Turn the heat on the cooktop to medium-low and melt the butter in a large high-sided skillet. Transfer the apples to the pan and cook for about 10-15 minutes, stirring occasionally. Adjust the heat lower if the apples are sticking or start to brown at the beginning of the cooking process.

When the apples have warmed through and softened some and most of the liquid has evaporated or thickened, then pour the caramel sauce into the pan with the apples. Stir to combine well and allow to heat through, reduce, and thicken. This will take about 10 minutes on a low to medium-low heat.

Spread the apple mixture into the crust in an even layer. Sprinkle with the remaining oat topping mixture. Bake for 40-45 mins or until the crust is lightly browned.

Let cool completely before cutting and serving. It can be placed in the fridge to cool down faster. Store bars covered at room temperature or in the fridge.