Preheat oven to 400°F. Line a rimmed baking sheet or jelly roll pan with foil and spray with nonstick spray. 

Line up the saltines on the prepared baking sheet so they are touching. Set aside.

In a saucepan over medium heat, bring the butter and brown sugar to a boil, stirring frequently. As soon as the mixture begins to boil, set a timer and boil for 3 minutes. Immediately remove from the heat and very carefully pour the mixture evenly over the prepared crackers.

Bake for 5 minutes. The sugar mixture will be very bubbly and the crackers will have started to float. 

Remove from the oven and use the tip of a knife to line the crackers back up if needed. Sprinkle the chocolate chips evenly over the top; return the pan to the oven for 1-2 minutes, until the chocolate is soft enough to spread.

Use an offset spatula to evenly spread the chocolate over the crackers. Sprinkle with the chopped pecans, if using.

Let cool completely. (Place the pan in the refrigerator if you need it to cool faster.) Break into pieces and store in an airtight container.