Preheat oven to 350°F. Spray a 9x13-inch baking dish with nonstick cooking spray.
To a large bowl, add butter, brown sugar, and vanilla. Using a hand-held mixer, cream ingredients until light and fluffy.
Add eggs one at a time, mixing until fully incorporated.
Add the flour, baking soda, and salt. Mix at low speed until combined.
Mix in the chocolate chips.
Press half of the cookie dough into the prepared baking dish in an even layer. Set the remaining cookie dough aside.
Bake for 15 minutes.
Carefully remove the cookie bars from the oven and place on a heat-safe surface.
Pour the warmed hot fudge over the bars, making sure to get it into every nook and cranny.
Using the remaining cookie dough, form small discs and place them over the top of the fudge. It is okay if there is some fudge showing through.
Bake for an additional 20-22 minutes, or until the fudge is bubbling and the cookie dough on top is golden brown.
After removing the bars from the oven, sprinkle the toffee bits evenly on top.
Allow bars to cool to room temperature (about 1 ½ hours) before cutting and serving.