Preheat the oven to 375 degrees Fahrenheit. Line a baking sheet with aluminum foil. Coat the covered baking pan with cooking spray.
Place graham crackers to cover the bottom of the pan. Set aside.
Put the brown sugar in a saucepan. Over medium heat, mix until the butter is melted and combined with the brown sugar.
Bring to a simmer, not boiling, for 2 minutes.
Pour the butter/sugar mixture over the graham crackers. Quickly spread evenly over the graham crackers.
Sprinkle the chopped nuts over the covered graham crackers.
Bake in the preheated oven for 5 minutes. Take the pan out of the oven. Quickly, sprinkle the chocolate chips over the toffee bars.
Place the toffee bars back in the oven. Bake for 2 minutes then remove from the oven again.
Leave the toffee bars to cool off completely, then break into pieces to serve.
Notes
Grease the baking pan: This will prevent sticking. Add the sweet butter quickly: You'll want to pour this over the graham crackers while it's still hot. Let them cool completely: This ensures they set firmly and can be broken into clean squares.