Preheat oven to 350°F. Line 9×13" jelly roll pan with aluminum foil. Spray foil with cooking spray and then line pan with saltine crackers.
Place butter in a medium-sized pot over low medium/low heat. Stir until butter is slightly melted, then add sugar. Once butter is melted, bring to a boil over medium-heat for 3 minutes, or until it thickens and sugar has dissolved. Stir constantly. You want the butter and sugar to be combined and turn an amber caramel color.
After 3 minutes, remove pan from heat and pour evenly over the saltine crackers. Spread mixture with a knife. Place pan in oven and bake for 7-8 minutes or until lightly golden brown. The mixture will spread evenly over the crackers as it bakes.
Remove pan from oven. If you're adding chocolate sprinkle the chocolate chips over top and allow to sit for 5 minutes (or place back in the oven for 1 minute). Then spread with a spatula and sprinkle with nuts if desired. Allow to cool.
Allow the toffee to cool and then break pieces off of foil or use a sharp knife to cut.
Notes
Storage: Store in a covered container at room temperature or in the fridge for up to 2 weeks. Freezer instructions: Store in a covered container and freeze up to 3 months.