Preheat oven to 350°F (175°C). Line a 10x15 inch rimmed baking sheet with aluminum foil and lightly spray with non-stick spray.

Arrange the saltine crackers in a single, tight layer on the prepared baking sheet.

In a medium saucepan, melt the butter and brown sugar over medium heat, stirring until combined. Bring the mixture to a rolling boil, then boil for exactly 3 minutes without stirring.

Immediately pour the hot caramel mixture evenly over the crackers. Bake for 12-15 minutes, until the caramel is bubbly and rich in color.

Remove from the oven and sprinkle the chocolate chips evenly over the hot caramel. Let them sit for 5 minutes to melt, then spread the chocolate into a smooth layer with an offset spatula.

Sprinkle with flaky sea salt. Allow to cool completely at room temperature or in the refrigerator until firm. Once set, break into pieces and serve.