Preheat the oven to 400 degrees, and line a 10" x 15" with foil (the kind of sheet that has raised edges!). Spray with Pam, or grease VERY lightly with butter. Cover the cookie sheet with a single layer of saltines. Bring butter and brown sugar to a boil. Boil for 3 minutes, stirring with a whisk. Pour over the saltines, and try to spread it as evenly as possible. Place in the oven and bake for 5 minutes. When you remove it, the caramel mixture will be molten and boiling; allow to cool about 3 min, or until you can see the crackers distinctly, which will have shifted while baking. Push them back into order with a fork or knife. Sprinkle the chocolate chips over the toffee and let sit for about 5 minutes to melt. Once melted spread chocolate evenly. If desired, sprinkle on pecans and press lightly into the chocolate. Let cool a bit and then transfer to fridge to harden. Once hard, break the candy into small pieces and place in containers.