Preheat oven to 350°F. Line an 8×8" or 9x9" pan with parchment paper, leaving over hang for easy removal later.
Combine the melted butter, brown sugar and vanilla, whisking until smooth. Add the 1 cup flour, oats, salt and baking soda. Stir to combine thoroughly and press half of this mixture into the bottom of the prepared baking pan. Pressing to edges and making sure it's as level as possible. Bake 10 minutes.
In a measuring cup melt the caramel and heavy cream together in a microwave, blasting in 1 minute intervals until smooth, or in a saucepan over medium heat. Whisk in the remaining 3 tablespoons of flour. Set aside.
Remove cookie base from oven and, sprinkle in layers the chocolate chips, nuts and caramel mixture. Crumble remaining half of oatmeal mixture over the top to cover. Bake for 18 minutes and top is golden brown.
Let cool at least 4 hours or overnight before cutting into 16 bars.
I prefer the caramel bits as they melt easier, but a bag of 35 caramel squares like Werther's Original are a fine substitute if you can't find. I also prefer not having to unwrap them. You can also make Homemade Caramel Sauce, too!