Preheat oven to 350F degrees.
Line a 13x18 baking sheet with foil. Coat the foil with nonstick cooking spray. Arrange the saltines on the baking sheet so that there are no gaps between them.
In a saucepan, melt the butter over medium heat. Once the butter is melted, stir in the brown sugar using a wire whisk. Continue to whisk the mixture over medium heat until it bubbles, thickens and becomes creamy. If using a candy thermometer, aim for a temperature of 295F-305F degrees.
Remove the toffee from heat and quicky stir in the vanilla and salt. Then, quickly pour it over the crackers and spread it out to cover. Bake for 5 minutes.
Remove from oven and quickly sprinkle the chocolate chips evenly over the toffee. Let them sit for 5-10 minutes, until they become glossy. Then, use an offset spatula to spread the chocolate over the toffee layer.
Add crushed pecans, Christmas sprinkles or melted white chocolate as decorations, if preferred.
Chill in the refrigerator at least 2 hours.