Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper. Make sure the parchment extends over the edges for easy removal later.
Arrange the saltine crackers in a single layer on the baking sheet, covering the entire surface.
In a medium saucepan over medium heat, melt the butter and brown sugar together, stirring constantly until the mixture comes to a boil. Once boiling, let it cook for exactly 3 minutes without stirring.
Remove the saucepan from heat and stir in the vanilla extract and salt. Carefully pour the hot toffee mixture evenly over the saltine crackers, using a spatula to spread it out gently.
Bake the toffee in the preheated oven for 5-7 minutes, until it is bubbling and starting to turn a light golden color.
Remove from the oven and immediately sprinkle the chocolate chips over the hot toffee. Let it sit for about 2 minutes to soften the chocolate, then spread it out evenly with a spatula.
If using nuts, sprinkle the chopped pecans or walnuts over the melted chocolate. Press them slightly into the chocolate for better adhesion.
Finish with a light sprinkle of sea salt on top for a delightful sweet-salty balance.
Allow the toffee to cool at room temperature for about 30 minutes, then refrigerate for at least 1 hour or until completely set.
Once set, break the toffee into pieces and store in an airtight container at room temperature.
Notes
Allow toffee to cool completely before breaking into pieces.