Arrange graham crackers in the bottom of a 15 1/2 x 10 1/2 inch jellyroll type baking pan.
In a medium sauce pan, combine the butter and brown sugar. Over medium heat, bring to a boil. Reduce heat to low and cook for 5-6 minutes, stirring occasionally.
Remove from heat and stir in chopped pecans. Pour mixture over graham crackers. Spread evenly.
Bake at 350 for 8-9 minutes.
Remove from oven to cooling rack. Scatter chocolate chips over the hot toffee. Wait for 1 minute, then spread the chocolate evenly over the toffee.
Let the graham cracker bars cool completely. I usually put mine in the fridge for a little while. When cooled I flip over the pan (using another jelly roll pan) so that the bars are upside-down, then I cut along the individual graham crackers.