Line a 10x15-inch rimmed sheet pan with foil. Top the foil with a layer of parchment paper. Lay the crackers, salt-side up into an even layer over the parchment paper.
Combine 1 cup unsalted butter and 1 cup brown sugar in a small saucepan. Bring the mixture to a boil over medium heat, stirring occasionally. Once the mixture comes to a boil, allow it to cook for exactly 60 seconds, while whisking constantly. The mixture should be a deep golden color. Remove from the heat, and stir in 1 teaspoon vanilla extract.
Drizzle the caramel mixture evenly over the crackers, spreading to cover if needed. Bake for 10 minutes. Remove the pan from the oven and turn the oven OFF.
Sprinkle the chocolate evenly over the crackers. Return the pan to the warm oven for 1-3 minutes, or until the chocolate is soft and glistening.
Remove the pan from the oven, and use an offset spatula to spread the melted chocolate evenly over the crackers. If desired, sprinkle with chopped walnuts or other candy over the chocolate while still warm.
Allow the mixture to cool to room temperature and then transfer the tray to the refrigerator to chill completely. This will take about 1 hour.
Once the chocolate has hardened, cut or break it into bite-size bars. Store the toffee candy in the refrigerator in an airtight container for up to 2 weeks.
Notes
Chocolate: Feel free to use milk or dark chocolate in place of the semi-sweet chocolate. Nuts: Use chopped walnuts, almonds, or pecans OR omit the nuts. Toasted nuts are best in terms of flavor. Note on Salt: If using unsalted saltines, you will want to use salted butter or stir in ¼ to ½ teaspoon of kosher salt to your caramel mixture when you add the vanilla extract. You need a bit of salt to balance out the sweetness in this recipe. Nutrition is based on 1/24th of the recipe without adding nuts.