Preheat the oven to 350F (180C) degrees. Line a 9x13 inch pan with parchment paper so that there's an overhang around the edges. Alternatively, line with foil and lightly grease.
In a large bowl, whisk together the melted butter, brown sugar and vanilla extract until evenly combined. Ideally, it won't look like the butter is separate.
Stir in the flour, baking soda and salt. Then stir in the oats.
Press about half of the mixture into the bottom of the prepared pan to form an even layer. Place the remaining half of the dough in the fridge. Bake in the preheated oven for about 15-20 minutes, or until golden on top.
Remove from the oven and cool for 10 minutes.
Sprinkle the chocolate chips on top to form an even layer.
Pour/ spoon the thick caramel sauce on top of the bars. I always use a very thick caramel topping and warm it up in the microwave slightly so that it's easier to pour.
Section off small bits of the remaining cookie dough. Flatten them down and place on top of the caramel sauce to form an even layer. If some caramel shows through, that's ok. Alternatively, you can crumble to remaining dough overtop.
Place the pan back in the oven and bake for about 15-20 minutes, or until the top is golden.
Cool the bars completely - this will take about 4 hours.
When ready to slice, carefully remove the bars from the pan using the overhang from the parchment paper/foil. Place on a cutting board and slice using a large sharp knife (not a table knife).