Preheat the oven: Set your oven to 400°F (200°C).

Prepare the pan: Line a 9x13-inch baking pan with aluminum foil, ensuring the edges are covered. Arrange a single layer of saltine crackers in the pan, covering the bottom completely. Set aside.

Make the toffee: In a medium saucepan, combine the butter and dark brown sugar. Cook over medium heat, stirring occasionally, until the mixture comes to a rolling boil. Allow it to boil for 3 minutes, stirring constantly to prevent burning.

Pour the toffee: Carefully pour the hot toffee mixture over the layer of saltine crackers, spreading it evenly with a spatula.

Bake: Place the pan in the preheated oven and bake for 7 minutes. The toffee will bubble as it cooks.

Add chocolate: Remove the pan from the oven and immediately sprinkle the chocolate chips over the hot toffee layer. Let sit for 1-2 minutes to allow the chocolate to soften, then use a spatula to spread it evenly like frosting.

Optional toppings: Add your desired toppings, such as chopped nuts, crushed candy canes, or a sprinkle of sea salt.

Cool and break: Refrigerate the pan until the toffee is fully set, about 1-2 hours. Once cooled, remove the toffee from the pan, peel off the foil, and break it into bite-sized pieces.

Serve and enjoy: Store the toffee in an airtight container at room temperature or in the refrigerator for up to a week.