Preheat oven to 375°F. Line a jelly roll pan with aluminum foil, making sure the foil covers the bottom and all of the sides of the pan. Spray the foil with baking spray.
Line the bottom of the foil lined pan with the saltine crackers.
In a small saucepan over medium heat cook the brown sugar, butter, and salt. Stir frequently. Once the butter is melted, bring the mixture to a rolling boil. Set a timer and boil the mixture for 3 minutes, stirring frequently. If using a candy thermometer or an instant read thermometer, the mixture should reach 265°F-275°F *
Pour the mixture over the saltine crackers and use a heat proof rubber spatula or off set spatula to spread the toffee in an even layer over the saltines. Bake for 5 minutes.
**See notes. Remove from the oven and sprinkle the chocolate chips (or finely chopped chocolate) overtop. Let sit for 3-4 minutes or until melty. ***Spread the chocolate in an even layer.
Let chocolate set.
Once chilled and cool, gently lift the foil from the pan cut the Christmas crack into bite sized pieces.
Store in an airtight container.