Preheat oven to 375 degrees. Line a baking sheet (with sides) with foil for easy clean-up. Arrange 40 saltines on foil, single layer, touching.
In a small saucepan, bring butter and brown sugar to a boil, stirring occasionally. Remove from heat and stir in baking soda. Pour over crackers, spread to coat evenly and bake 6 - 8 minutes.
Immediately sprinkle chocolate chips over, then as they warm up and start to melt, spread with a rubber spatula to cover. Let cool completely (you can speed up the process by putting it in the refrigerator) and break into chunks. Store covered at room temperature for up to a week.