Preheat oven to 350°F. Line a rimmed baking sheet with parchment paper or a silicone baking mat (or aluminum foil sprayed with nonstick cooking spray). Line the saltine crackers up in rows on the prepared baking sheet. Set aside.
Add the butter and brown sugar to a large saucepan over medium heat. Stir until the butter is completely melted and bring to a boil. Once boiling (the top should be completely covered in bubbles), stop stirring and allow to boil for 3 minutes.
Remove from the heat and carefully pour over the crackers on the baking sheet. Transfer the baking sheet to the oven and bake at 350°F for 5-8 minutes or until the toffee layer is bubbling.
Remove from the oven, sprinkle the chocolate chips on top, and allow to sit for 5 minutes to melt. Spread the chocolate over the toffee with an offset spatula or the back of a spoon, then sprinkle the chopped pecans on top.
Transfer to the refrigerator to chill for 30-45 minutes. Break into pieces, serve, and enjoy!