Preheat the oven to 400°F (200°C). Line a 10x15-inch jelly roll pan with nonstick aluminum foil or heavy-duty foil coated lightly with nonstick spray. Arrange the saltine crackers in a single layer across the bottom of the pan, ensuring full coverage.

In a medium saucepan, combine the brown sugar, butter, and salt. Place over medium heat and cook, stirring frequently, until the butter is fully melted and the mixture becomes smooth. Continue to cook for 3 to 5 minutes, stirring constantly, until the mixture begins to boil and darkens slightly in color. Do not allow it to boil for more than 30 seconds. Remove from heat and immediately stir in the vanilla extract.

Carefully pour the hot brown sugar mixture over the saltine crackers, spreading it evenly with a heatproof spatula to ensure complete coverage.

Transfer the pan to the preheated oven and bake for 5 minutes, or until the caramel is bubbling vigorously across the surface. Remove from the oven and allow to cool for 1 minute, until the bubbling subsides.

Place the chopped chocolate in a microwave-safe bowl. Heat in 30-second intervals, stirring after each round, until the chocolate is fully melted and smooth (approximately 1½ minutes total).

Pour the melted chocolate over the slightly cooled caramel-covered crackers. Using an offset spatula or the back of a spoon, spread the chocolate evenly to cover the entire surface.

Allow the pan to cool to room temperature, then refrigerate for at least 8 hours or overnight to allow the chocolate and caramel to fully set.

Once chilled, lift the candy sheet from the pan and peel away the foil. Break or cut into irregular pieces using a sharp knife. Store in an airtight container in the refrigerator for up to one week or freeze between layers of parchment paper for up to two months.