Preheat oven to 350 F. Line a 9◊13-inch pan with aluminum foil and spray with cooking spray.
Place graham crackers in pan in a single, flat layer so pan is completely covered with them. You will have to break some crackers to fill in the smaller spaces at the edges. Itís ok if there are slight gaps, doesnít have to be perfect; set aside.
To a medium, heavy-bottomed saucepan with high sides, add the butter, brown sugar, salt, and heat over medium-high heat to melt. Stir constantly until butter has melted.
After butter has melted, allow mixture to boil for about 4 1/2 to 5 minutes at a medium-fast boil (lots of bubbles). Stir constantly to prevent burning. As you approach the 4 minute mark, mixture should seem thickened with the consistency of medium-thick caramel sauce. I pulled mine off the heat at 4 1/2 minutes because it was thick enough.
Evenly pour mixture over graham crackers.
Bake for about 7 minutes, or until thereís bubbling around the edges.
Remove pan from oven, evenly sprinkle with chocolate chips, return pan to oven, and bake for about 2 minutes, or until chocolate chips are glistening and have softened.
Use a spatula to smooth the chocolate chips into an even, smooth layer of melted chocolate.
Allow toffee to cool for about 2 to 3 hours, or until chocolate has set.