Preheat oven to 350°. Line a 2 15x10x1-in. baking pans with foil. Arrange crackers in pan; set aside., In a large heavy saucepan over medium heat, melt butter. Stir in brown sugar. Bring to a boil; cook and stir for 3-4 minutes or until sugar is dissolved. Spread evenly over crackers. , Bake at 350° for 15-17 minutes (cover loosely with foil if top browns too quickly). Sprinkle with chocolate chips; let stand 5 minutes. Spread chocolate over top. If desired, sprinkle with salt. Cool in pan on a wire rack for 1 hour. , Break into pieces. Cover and refrigerate for at least 2 hours or until set. Store in an airtight container.