1. Preheat the Oven:
- Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan and line it with parchment paper, leaving some overhang for easy removal.
2. Make the Oat Mixture:
- In a large bowl, combine the melted butter, brown sugar, and vanilla extract. Stir in the flour, oats, baking soda, and salt until well combined.
3. Assemble the Bottom Layer:
- Press half of the oat mixture evenly into the bottom of the prepared pan. Bake for 10 minutes, then remove from the oven.
4. Prepare the Caramel Filling:
- While the bottom layer bakes, mix the caramel sauce with the heavy cream in a small bowl.
5. Layer the Filling:
- Sprinkle the partially baked crust with the chocolate chips and nuts (if using). Pour the caramel mixture evenly over the top.
6. Add the Topping:
- Crumble the remaining oat mixture over the caramel layer, spreading it as evenly as possible.
7. Bake:
- Return the pan to the oven and bake for 18-22 minutes, or until the top is golden brown and set.
8. Cool and Serve:
- Let the bars cool completely in the pan. For clean cuts, refrigerate for at least 1 hour before slicing. Remove from the pan using the parchment paper overhang, slice into squares, and serve.