Preheat your oven to 350°F.

Line a 9x13'' pan with parchment paper or spray with cooking spray.

Place the graham cracker sheets to cover the bottom of the pan.

In a large saucepan over medium heat, melt the butter. Add the brown sugar and chopped pecans, stirring constantly. Bring the mixture to a full boil.

Boil for 5 minutes, continuing to stir constantly.

Remove from heat and pour the mixture over the graham crackers, spreading it into an even layer.

Bake for 7 minutes.

While the bars are baking, unwrap the Hershey's chocolate bars and break them into pieces.

Remove the bars from the oven and place the chocolate pieces evenly across the top of the toffee layer. Cover the pan with a lid or aluminum foil to let the chocolate melt for about 5-10 minutes.

Once the chocolate has melted, use a spatula to spread it evenly over the bars.

Allow the bars to cool completely before serving. For a firmer texture, store them in the fridge to set up. Before cutting, leave them out at room temperature for about 15 minutes to let the chocolate soften.