Cover the whole sheet with crackers (I did 6 across and then 8 down and then cut three more in half and it fit perfectly)
In a medium-sized saucepan, cook the butter and brown sugar together over medium heat, stirring frequently to keep from burning. Once it comes to a boil, set the timer for three minutes and stir pretty much constantly. When the timer goes off, take the pan off the heat, add the salt (if you're using it) and the vanilla, give it a quick stir, and then immediately pour it over the pan of crackers, gently spreading it evenly with a rubber spatula so that all the crackers are covered.
Put it in the oven and bake for about 10-12 minutes, keeping an eye on it so it doesn't burn, especially around the edges.
When it's done, sprinkle all the chocolate chips on top and let them melt for 3-5 minutes. Once they are melted, spread them with a spatula to make a smooth chocolate layer and sprinkle the nuts and sea salt over the top.
Cool in the fridge until the chocolate is completely solid, then break into pieces and eat (or. . . you know, give it as gifts. Your call).