• Preheat the oven to 350°F. Prep an 8x8 baking pan with non-stick spray. Spray both the bottom and the sides. For easier release, you can even use parchment paper with extra paper hanging over the sides.

Prepare the crust:

• In a large bowl, combine the flour, sugar, cinnamon, salt, and vanilla extract.
• Add in the cold, cubed butter. Use your hands or a pastry cutter to work it into the dry ingredients until the mixture looks crumbly.
• Press the mixture firmly into the bottom of the baking pan. I like to use the bottom of a measuring cup to push the crumbs into the bottom of the pan pressing it in to make sure you have a sturdy base for the bars.
• Bake for 15 minutes, or until it's set and the edges are very lightly brown. When done, take out of the oven and let it slightly cool.

Prepare the apple filling:

• In the same large bowl, mix together cornstarch, brown sugar, cinnamon, nutmeg and salt.
• If your apples aren’t already sliced, peel them and cut into thin slices. I like to halve the slices lengthwise to make them bite-sized—perfect for bars.
• Toss the sliced apples in the mixture until evenly coated.
• Spread the apples evenly over the cooled crust.

Make the streusel:

• In a small bowl (or the same bowl), combine oats, flour, and brown sugar.
• Add the cubed butter and work it in with your hands or a pastry cutter until the mixture forms a crumbly topping.
• Sprinkle the streusel evenly over the apples.

Bake:

• Bake for 40 to 45 minutes, or until the apples are fork-tender and the topping is lightly browned.
• If the streusel browns too quickly, loosely cover the pan with foil forming a tent over the baking pan.
• Allow the bars to cool completely in the pan before slicing. About 30 minutes to an hour.

Caramel:

• In a heavy-bottomed pot, melt butter and sugar over medium-low heat, stirring occasionally. Once bubbling and golden (about 10 minutes), reduce heat and whisk in cream carefully. Cook 4–5 more minutes until it reaches 225°–230°F.
• Remove from heat, stir in vanilla and salt, then pour into a heatproof bowl. Cool for 15–30 minutes before using.
• Serve with Caramel
• Drizzle with salted caramel sauce just before serving. If caramel sauce is refrigerated, gently reheat the sauce in 15–20 second intervals in the microwave to loosen it up.