Preheat oven to 400 F. Line a 10x15-inch rimmed baking pan (jelly roll) with parchment or a silicone baking mat.
Lay the crackers in an even layer across the bottom of the baking pan.
In a medium saucepan over medium heat, bring butter and brown sugar to a boil.
Let boil, whisking regularly, for 2-3 minutes.
Remove from heat, and stir in vanilla.
Carefully pour toffee over crackers, and spread toffee over crackers.
Bake for 5-6 minutes.
Remove from oven, and sprinkle chocolate chips over crackers.
Let stand 5 minutes.
Gently spread chocolate over crackers.
Sprinkle with chopped pecans and sea salt, if using.
Let sit at room temperature for 1 hour.
Chill or freeze for 20 minutes.
Break or cut into pieces.
I recommend using regular, salted Saltine crackers.
I don't pack the sugar. However, if you like the toffee sweeter, you can. Also, I use dark brown sugar for a richer toffee flavor. You can use light brown sugar, but it won't have as much toffee flavor.
I use bittersweet chocolate chips to keep the toffee from being too sweet. However, you can use anything from milk to semisweet to bittersweet in this recipe.