Preheat the oven to 425 degrees F. Line 1 large or 2 small jelly-roll pans with aluminum foil, spray with nonstick spray and arrange the saltines salt-side down in a single layer. In a medium saucepan, melt the butter and brown sugar together and boil until it turns a caramel color, a few minutes. Remove from the heat and pour over the crackers, covering them evenly. Put the jelly-roll pan into the oven and bake for 3 to 5 minutes, or until just bubbly, watching carefully. Remove from the oven and pour the chocolate chips over the crackers. When the chips melt a bit, spread them over the crackers with a knife. Transfer the pan to the freezer for 15 to 20 minutes, or until completely cold. They will form one big sheet. Break up into pieces. Store in an airtight container.
Recipe adapted from Home Cooking with Trisha Yearwood (c) Clarkson Potter 2010