Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper, ensuring you have enough overhang for easy removal later.
Arrange the Saltine crackers in a single layer on the prepared baking sheet, covering the entire surface.
In a medium saucepan, melt the butter over medium heat. Once completely melted, add the brown sugar and stir continuously until the mixture comes to a gentle boil. Allow it to boil for 2-3 minutes without stirring.
Pour the hot toffee mixture evenly over the Saltine crackers, spreading it gently with a spatula to cover all the crackers.
Bake in the preheated oven for 5-6 minutes, or until the toffee is bubbly and golden.
Remove the baking sheet from the oven and immediately sprinkle the chocolate chips evenly over the hot toffee. Let them sit for a few minutes until melted.
Once melted, use a spatula to spread the chocolate evenly across the toffee. Sprinkle with chopped nuts and a light pinch of sea salt.
Allow the toffee to cool at room temperature until firm, or place it in the refrigerator for about 30 minutes to speed up the process.
Once completely cooled, break the toffee into pieces of desired size and serve or store in an airtight container.