Step 1

Arrange a rack in the middle of the oven and heat to 350°F. Line a rimmed baking sheet with aluminum foil. Arrange the saltine crackers in a single layer on the baking sheet.

Step 2

Place the butter, sugar, salt, and vanilla in a 2-quart saucepan and bring to a boil over medium-high heat. Reduce heat to medium and cook, stirring just a few times, for 3 minutes. The mixture will be thickened slightly and homogeneous.

Step 3

Working quickly, pour the hot toffee mixture over the crackers, spreading it so most of the crackers are completely covered.

Step 4

Bake until the toffee is bubbling and both the crackers and toffee are beginning to brown, about 15 minutes.

Step 5

Remove the pan from the oven and immediately sprinkle with the chocolate chips. Let the chocolate melt for 5 minutes, then use a spatula to spread the chocolate into an even layer. Set aside to cool for at least 2 hours before cutting into 30 pieces.