1. Preheat the oven to 400F. Line a 10x15-inch jelly roll pan with nonstick aluminum foil (preferred) or regular heavy duty foil, making sure that the foil completely covers the bottom and sides of the pan. If using regular foil, spray lightly with baking spray. Line the saltine crackers in a single layer on the bottom.
2. Make the caramel sauce. Place the brown sugar, butter and salt in a medium sized saucepan. Cook on medium heat, stirring frequently, until the butter melts. Continue to cook, stirring occasionally, for another 3 to 5 minutes, just until the mixture comes to a boil and starts to darken. Remove from heat and stir in the vanilla extract.
3. Pour the hot brown sugar mixture over the saltine crackers. Spread to evenly coat the crackers.
4. Move the pan to the oven and bake for 5 minutes. The caramel will be hot and bubbly.
5. Melt the chocolate. Place the chocolate in a microwave-safe bowl. Cook it in the microwave in 30-second intervals at full power, stirring between each cook time, until the chocolate has melted.
6. Pour the chocolate over the baked crackers. Once the crackers are done baking, remove from oven and allow to cool for 1 minute, until the caramel is no longer bubbling. Then pour the melted chocolate over the crackers. Use a spatula to spread the chocolate evenly over the top.
7. Cool the crackers overnight. Let the crackers cool to room temperature then move to the refrigerator and cool over night.
8. "Crack" the crackers. The crackers will form a single sheet once cool. Remove from pan and gently peel the foil away, being careful not to tear the foil. (If any bits of foil tear and get stuck in the caramel, break those bits away and discard.) Cut the candy into snack-sized pieces using a chefs knife (you can use your hands, too, but I find it easier with a knife).