Preheat your oven to 400 degrees Fahrenheit. Line a large rimmed baking sheet with parchment paper or a silicone baking mat. This step is crucial because the toffee will become very sticky, and you want to ensure the cookies lift off the pan easily once they have set.
Arrange the saltine crackers in a single layer on the prepared baking sheet. You may need to break a few crackers to fit the edges of the pan, but try to keep them as close together as possible without overlapping. This creates the “cookie” base for your treats.
In a medium saucepan, combine the unsalted butter and the light brown sugar. Place the pan over medium heat and stir constantly until the butter has melted and the mixture begins to boil. Once it reaches a boil, let it bubble for exactly three minutes without stirring. After three minutes, remove from heat and carefully stir in the alcohol-free vanilla extract.
Pour the hot toffee mixture evenly over the crackers, using a spatula to spread it to the edges so every cracker is coated. Place the baking sheet in the oven and bake for 5 to 7 minutes, or until the toffee is bubbling across the entire pan. Watch it closely to ensure the edges do not burn.
Remove the pan from the oven and immediately sprinkle the chocolate chips over the hot toffee. Let them sit for about two minutes until they look soft and glossy. Use an offset spatula to spread the melted chocolate into an even layer across the top of the cookies.
While the chocolate is still warm, sprinkle the chopped nuts and sea salt over the top. Allow the pan to cool at room temperature for about 30 minutes, then transfer it to the refrigerator for at least two hours to set completely. Once firm, break or cut the slab into individual cookie-sized pieces.
