Preheat your oven to 400F (205C) and line a standard-sized cookie sheet with foil. Lightly spray with cooking spray or grease lightly with butter.

Layer crackers evenly over the foil (salted side up); it's alright if there are spaces between the crackers and not every edge is completely filled in.

Prepare your toffee by combining butter and brown sugar in a small saucepan over medium heat, stirring occasionally.

Allow mixture to come to a full rolling boil and allow it to boil for three minutes -- stir only occasionally/as needed to prevent burning.

Immediately remove from heat and pour over crackers (it's ok if some of them start to float, just try to keep them in an even layer), spread with a heatproof spatula to completely coat crackers.

Place in 400F (205C) oven for 5 minutes -- toffee will begin to bubble.

Remove from oven and turn off the oven. Evenly sprinkle chocolate chips over the hot toffee. Return tray to the oven for two minutes, then remove and use a spatula or knife to spread chocolate evenly over crackers.

Sprinkle evenly with chopped pecans (or preferred topping -- or no topping!) and a scant amount of flaky sea salt (if desired).

Allow to chill in refrigerator for at least 30 minutes or until chocolate hardens. Cut into pieces using a large knife and serve.